How less onerous free can be?

If you are talking about time.... At least half of the time spent to compare trial versions is not lost since a program will be (hopefully) selected. As to you tube to compare? Not a good idea at all. You either have all out commercials for both programs or more or less competent folks offering tutorials. YouTube videos do not present capabilities or limitations of any program but the skills (or lack of it) of the presenter.

Now the amount and quality of tutorials can be a factor when making decision.

I apologize over this reply but one has to say what is what when it comes to making a choice. I just felt that some elements of your post where misleading.

Welcome to the forum Sam.
Your question 'fx (full frame) or mirrorless' question is a bit confused. You are comparing apples to oranges. You should be asking two seperate questions - (a) DSLR or Mirrorless and (b) Full Frame or Crop Sensor.
(a)
DSLRs are built around the technology of the film era SLR cameras with viewfinders using prisms and flapping mirrors. They give a nice clear immediate image in the viewfinder. The image you see is coming from the lens (TTL), not the sensor so you are not actually seeing what the the camera is going to send to the memory card. Mirrorless gives a viewfinder image digitally generated by the sensor and 'engine'. Mirrorless gives a 'what you see is what you get' (WYSIWYG) image. Earlier versions of mirrorless tended to be grainy and had a lot of lag. The latest one are big, bright, clear and fast.
Note that the choice of viewfinder only effects your ability to visualize the shot and compose the picture. It doesn't directly effect the image quality. DSLR's tend to be heavier and bigger than Mirrorless. Many photographers of advancing years are switching to Mirrorless because they can no longer haul their DSLR's around all day. Mirrorless is the only growing segment of the market. Some would disagee, but DSLRs are often considered to be the technology of the past, whereas Mirrorless is the technology of the future. The most frequent reason I see here for not switching to DSLRs is that they have too much money invested in their DSLR system to consider changing. For a newbee unencumbered by a lifetime of legacy gear, I think your first choice should be mirrorless.

(b)
DSLR' come in 'Full Frame' sensor size and in 'crop' APS-C sensor. Mirrorless come in Full Frame, crop APS-C, the smaller Micro 4/3, and even in a larger 'medium' format. Full Frame will generally give a marginally better image than a crop sensor of the same generation. By that I mean that some newer crop cameras are capable of giving better images than some 5 year old FF cameras. If you are considering buying a used camera - age matters. By 'marginally better' I mean the differance may only be noticeable if you are printing very large prints, close crops, shoot in the dark or are a pixel peeper. For the most part, the benefit of FF is only in the range of 1 or 2 stops of light. FF cameras require FF lenses which are bigger, heavier and more expensive than equivalent field of view crop lenses. You will get more 'bang for your buck' with an APS-C or M4/3 system.

I think your budget is a bit reversed. I would plan on spending less on the body and more on the lenses. Look for a body with image stabilization. Set some money aside for a good circular polarizing filter and a decent tripod. Sony and Fuji are the leaders in aps-c mirrorless. Olympus and Panasonic are the leaders in M4/3. Focus your research on these systems.