You don’t have to worry about thermals, but also, the 512 is fine, I have the 256 and just keep content externally.

Spend the money you could have upgraded with to get an even bigger external drive. I’m an artist and musician that runs two bands, and my solo work. I do video art that takes up a LOT of space (for instance, I shoot video, then run it through video synthesis, then edit for a final output, and each if those steps creates new files taking up space). Apple sells upgrades for way too much, just put your content, instrument library, effects plugins, etc on external drives.

I’ve never even heard the fan come on and I use programs like touchdesigner, adobe suite, OBS, Logic, NDI tools, etc and sometimes many at the same time. And, I have mine mounted inside a rack system for live production that is full of other gear creating heat. Thermal throttling won’t be an issue.

As far as RAM, just learn to handle your projects appropriately. Freeze and bounce tracks. Turn off inputs on tracks that aren’t being used. Use bussing to keep plugin use down. Etc. You will be able to push it until you run into issues, but them you’ll end up in forums asking what to do and you’ll just learn that you need to do proper project management. So, look into it now and save yourself the headache.