Try all the ones that interest you, stick with what you like. After distrohopping for a while I landed on Fedora. I prefer it slightly to OpenSUSE but that is a good option too.
Calling it a "relatively small subset of the Steam library" seems like a bit of a stretch. Proton is promising, and it doesn't seem like performance will be an issue for the vast majority of Steam games.
I've managed to do it, but my path was a little different from yours. I didn't have any luck finding a job after finishing my CompSci degree, and ended up taking an application support role a few months after college out of desperation. I did that for about 2 years, and then ended up picking up an entry level development job at a different company in the same area.
The easiest way is probably to switch roles internally, but that wasn't much of an option for me, and doesn't sound like an option for you either.
What worked for me was looking for roles at growing, non-tech companies. I looked for companies with a large IT department, where their core business isn't to sell the technology you will be producing (so internal tools and such). These might not be the "best" roles long term but this should help you get your foot in the door, which is what you need more than anything at this point. These sorts of companies seem to be less picky about qualifications, and in my experience seem to be more likely to pick up inexperienced candidates to "grow with the team" especially if they already have established a decent amount of senior-level talent internally.
As far as how to sell yourself, my advice here is to sell yourself as former support analyst who is passionate about development and wants a career change, plain and simple. Six years of technical support will make recruiters want to push you into a support role, so get used to that. Be sure to make them aware of the development experience you got on the job as well as your side projects, and definitely lay it all out on your resume, but there's nothing wrong with being in support and wanting to switch to development. Own it, and let them know what advantages your support experience gives you that other developers won't have.
You make a decent point. This is why I mentioned a saliva test, but in truth I'm not sure how effective it is. Anecdotally, I can tell you I once smoked at night before bed and passed a saliva test the next morning.
As marijuana becomes increasingly legalized, I'm not sure why any company would continue to test for it, other than maybe using saliva tests to make sure workers aren't getting high on the job.
As long as you have a good pile of savings to fall back on, fuck it, YOLO the fuck out of your life. Why not right? Worst case you can always go back to wage slaving.