I think a Shopping Trolley might be ideal for your needs (and handy for, well, shopping, the rest of the time.)
If you want to push rather than pull it, you'd want a four-wheel one like the one below (can always pad it out with an old blanket or a couple of towels if it rattles too much.
Two wheeled ones are easy/quicker to move but you might prefer being able to rest on the handles and push?
This is just one example, if you Google for Shopping Trolley, you'll see loads at various prices.
(There are also some with built-in seats - not sure how practical they'd be for your requirements.
Happy shooting!
https://www.ebay.co.uk/itm/202387647023

Or you could use Microsoft Paint and get anthing you want in the pic.

.

You won't see the "freeze" as you take the shot because you don't see the shot you take - the old maxim "If you saw it - you missed it." (Mirror flips up during capture of the image.)
Check your manual for VC modes - some lenses offer an extra stop of stability when VC kicks in only for the shot, depending on which mode you select.(Also uses less power - battery lasts longer - but harder to see the pic and to focus.)
If you want to check the VC and see what it's doing for you, make sure you shoot a static subject - a building / statue - that's about it. Would try putting it on shutter priority and shooting a three-ish shot burst at 1/2x focal length, then 1/ focal length, 1/ half the focal length, 1/ a quarter... and so on and see the difference.

Bear in mind, any image stabiliser does nothing for a moving subject - it reduces or eliminates camera movement but it can't do anything for something moving relative to the rest of the frame.

A longer fast lens is also used to reduce Depth of Field - helping to make the subject "pop" out from a bunch of other people who are also in the frame.
(e.g. With four important people at a desk - you can go round the side and get a profile pic of each, nicely isolated but in context.)
One of the reasons a 70-200 f2.8 is such an indispensable bit of kit.

Don't know who said that about aperture but I wouldn't listen to them - all three parts of the "exposure triangle" affect the brightness / "exposure" of the image that results. Boosting any one of them will increase light, but at a cost to the image.
Shutter - how long the sensor catches light for. Slower shutter lets in more light but allows the camera and subject to move more, so more blur.
Aperture - size of the hole letting in light. Bigger aperture / hole (small fnumber, annoyingly) lets in more light but with less depth of field and so fewer things in focus.
ISO - amplifies the signal from the sensor to make it brighter. (Unlike other two, doesn't affect actual light getting to the sensor, it just acts like "gain" in an audio amp. Makes the image brighter (as if you'd let in more light) but because it amplifies what is sent from the sensor, any "noise" is also amplified.
(All of these can be used creatively, of course, slower shutter give impression of movement where a fast one "freezes" action so doesn't get the feel of moving, shallow depth of field allows you to choose what it is in the image that is sharp and it stands out from the rest / "pops". ISO - more for shooting when otherwise there just isn't enough light. Not aware of anyone who likes the noise - it's not exactly like film grain - but there are things you can do in post that make it look like old film.)

No! If you have ISO (or anything else set to Auto) you're not really in manual. But I don't say that as a purist.
If you want to know what effect changing each setting has, having anything on Auto will stop you from seeing the change in brightness. The camera will change the setting that *it* controls to aim for what it thinks is a good exposure. You won't see the effect on light when you change your aperture or shutter because the camera will change the ISO in the opposite direction to keep the final image at the same brightness.
I grew up with film, so the sensitivity (ASA but same difference as ISO) was fixed when you loaded the camera. The upside of this is that you only needed to learn two settings - aperture and shutter - since you didn't control the other one.
If you're starting out with manual, I'd suggest: set ISO to something fixed, say 200 (a classic film speed for a not very bright day) and then experiment with the other two settings to see what they do. (See below for more.)

If you usually shoot Auto ISO, no reason to change for a longer exposure. (If it goes so high that the resulting noise is hideous, you'd just make the exposure longer still.)
With film, there's an issue of Reciprocity Failure in low light / long exposures where, beyond around a couple of second it's not getting enough photons to react with the chemistry and the standard "exposure triangle" doesn't work. (e.g. opening up another stop or doubling the exposure duration doesn't make the image twice as bright - instead, you have to make a much bigger adjustment to get enough light in than you would expect and it gets proportionally worse the slower the exposure is.)
Good news - it doesn't particularly affect digital sensors, so shoot away.
(FWIW, I tend to shoot full manual but I'm not going to go on a moral crusade about it. Do what gets the results you want.)

You make a fair point and one that is often worth remembering in a number of situtations.
Just leave Equivalent Focal Length alone!! (Please :) )
EFL does a really useful, almost universal, job for 'togs working with cropped sensors: it describes, accurately, the change to the size of the visual field - nothing more, nothing less.
That allows people to make buying decisions between lenses and to consider composition and framing before a shoot. It's good.
Maybe if your post were headed "Equivalent Focal Length: it's not all you need to know." Or something.
What you describe - useful for cropping, printing and display - is not about the lens: it's principally about sensor resolution, which can then be related back to EFL in a formula which will, admit it, scare off people who are not comfortable with mathematics.
By all means, promote a new measure of "Pixel Equivalence" "Lens Resolution Capture" or the like - it *does*, absolutely, have its uses. (In a similar way to dxo's theoretically complex but practically useful PMpix measure, come to think of it.)
But maybe leave focal length equivalence alone - it's more than enough for a lot of people to deal with.

The manufacturer's stated ISO and the real ISO for the camera are two different things - they're allowed a certain amount of wriggle room which, typically, they use to make the camera look better than it is on paper.
Typically, measured "true" ISO is lower than what you set on the camera (so you get a better quality image at that ISO "setting").
Didn't think there'd be a difference between models from the same manufacturer but there certainly is in your case - not a vast amount, less than a stop, but a fair bit.
I looked up a comparison of your cameras on dxo and it might just be enough to explain it, especially if the way the camera computes accurate exposure has changed at all (and even if it hasn't.)
When the camera sets the exposure, it doesn't try to nail a "perfect" exposure for a scene - there isn't one, it's always a matter of judging the scene overall and going for aperture triangle that is closest to best average exposure across the frame.
In your case, there's nearly 100 "real" ISO of a difference between what the sensor is actually giving you at 400 and nearer 200 at the 800 setting: that could be enough for the computer to aim for the next ISO setting up.
Add in any differences in lighting between shots between the cameras, and any psychology at play (you might feel it's worse than it is because you feel it's a drop in performance) and maybe differences in what the processor thinks is the best exposure and that could explain it.
But it's not "just you" - there *is* a difference in the cameras and quite possibly enough to do what you describe.
#notjustyourage
(If you hover your cursor over the various dots on the charts, you'll see that measured ISO vs what the camera claims. Also look at how close the old camera's real 400 is to the new one's real "800".)
https://www.dxomark.com/Cameras/Compare/Side-by-side/Canon-EOS-77D-versus-Canon-EOS-700D___1156_870

Think OP is confusing their terms.
Looks like you're cropping the picture (zooming is what you do with a lens when taking a picture).
That smaller section has to be magnified more to fill the same size of print. If it's a tight enough crop (small enough part of the image) the resulting magnification of the noise ("grain" in film days) that was too small to see when looking at the full image is now visible. If you blow it up enough, you'll see the pixels that make up the image. (The size of the noise "grains" varies, depending on how noisy the picture was to begin with, largely the result of using higher ISOs.)
If the image was sharp, the crop is also sharp - it's just noisy for the reasons others have said re: magnifying the noise and possibly magnifying the pixels (dots that make up the image) to the point where you can see them.

It would, with a steady hand.
IS not necessarily "necessary" for a lot of people but, yep, can be handy.

Had this lens for a few years now.
So sharp even a Pro mate went "Shiinggg!!! This is SHARP!"
Pretty fast, plenty of opportunity for shallow Depth of Field.
Chromatic Aberration is pretty bad but easily resolved completely in post.

While I like the second better, it's not a photograph - it's a composite.
And still a nice picture.
As long as you're not telling people it's a photograph (and just putting it up without noting it's a composite would be doing just that) then it's absolutely fine.
Nice image, if you wanted to sell it as a poster or whatever else, that would be fine - people would be buying the image however it was made.
(The extra processing you did in the bird and the tree would also look good applied to the original photograph on its own, FWIW.)

Ah!
Thanks, Stephan.