Before you buy the Panasonic 100-400 you might want to know that this is a disposable lens. If it quits or gets damaged, you basically have to buy a new one. See the discussion at.
https://www.uglyhedgehog.com/t-558950-1.html
If you want a full frame, get a used 5D3. If you want a cropped sensor, the 7D2 is a fantastic camera. I have 170,000 shots on mine and it's still like new condition. If you get a good used 7D2 you can be well under your budget and you can sell it in the future for a good price. It is a big upgrade from a T3. I have a 60D, 7D, 7D2, 5DS-R, and 1DX2 and the 7D2 gets 80% of the use.
This is a very informative post. A 2 y old lens that costs $1700 is a disposable lens because they won't repair stuff? My 1993 Canon lens can be repaired it I needed to. Was toying with the idea of the G9x system but that will never happen. Will not buy Panasonic or recommend anyone else to. Would suggest that anyone that wants to jump on the latest mirrorless bandwagon to read about repair and support history of the different vendors
Welcome to Panasonic repair and support
A DSLR in Live View is mirrorless. Same light path and process. The mirror is flipped up out of the way so it is out of the light path. The DSLR live view will show on the screen the same thing you see on a " mirrorless" camera.
The 200-400 is an amazing lens but weighs more and costs more than the 500 F4 (3.62 kg as opposed to 3.19 kg) so the 100-400 ii is a much lighter option at 1.64 kg
I know the question is on mirrorless, but on a Canon DSLR you can get a similar view if you set it to live view and screen brightness to manual at a setting 1 below max. What you see in live view will be almost identical to the captured image. You will have a real hard time seeing the difference.
The 100-400 L ii is a fantastic lens and much improved optics over the series i. The 70-200 does not have enough reach for most wildlife. If you want maximum reach with the 100-400 you can use the 1.4x tele iii and/or get a 7D2 as a backup body. I have. 500 F4 ii but don't take it on long plane trips because if the size and weight.
If you could get a 6 year old Ferrari for the same price as a 2 year old Volkswagen, which woukd you buy? 5D3 all the way
I have both the 500F4 ii and the 100-400 ii and a 1.4x iii. I do mostly birding so the 500 with the 1.4x and 7Dmk ii is my go to lens. It is always handheld and I have gotten tack sharp keepers down to 1/25 s. I generally shoot at 1/100s or above if stationary birds and around 1/1600 for BIF. I use the 100-400 with 7D2 as my travel lens. If I take both lenses then I take my 1DX2 on one of the lenses and carry both of them. These lenses are all microfocus adjusted to each camera. The 500 with the 1.4x is still sharper than the 100-400 at 400 without the TC. These tests were done in an automated test system and graphed at each aperture setting so they are NOT subjective guesses. Both lenses are about as good as it gets for long reach with high quality images. I have never tried aftermarket lens and don't ever anticipate doing so when you can get this sort of quality with an OEM lens.
Delta 100 or T-Max 100 are very nice fine grain films and easy to develop yourself
The Canon 10-22 lens is a good option. Pick up a used one for a reasonable price. Very good landscape lens
Use Picture Information Extractor. It's free
My advice is if you have to ask, you will not want to mess with it. It's a PITA if you are a non-tech geek. And yes I have installed it and used it before