I think you can keep using the demo too. It has all the features and it even lets you save files, but you won't be able to reopen files if it made use of any of the plugins in demo mode.
"I think my mistakes have made it take about 5 times longer than it should have, but there's close to no info at all out there that I've found, so it's all trial and error, it's taken me weeks so far. "
Thats pretty much the way I learn this stuff

I normally use PMC, the pathtracing was just for the animation. Though I'm still just leaving it at the default values. Thought there might have been a "remove grainy" button that I missed

I've been planning to try out the settings... later... always later

Thanks for letting me know about the swimsuit. It is still showing as being in QA for me, so maybe they aren't done yet. I'll check to see what is going on (though I fear that for this time the textures might have to be downloaded again, but hopefully not for following updates)