There's a lot of really knowledgeable people here. Please correct any misconceptions that I may have...
it seems to me that I can take some 8/5 cable and a 5pin male plug and I can wire my 3phase air compressor to plug into that 5pin port, from where it will happily slurp 208v 3phase power. This is basic and obvious unless I am missing something equally basic and obvious.
It seems to me, that when I'm not using the 3phase air compressor, and I want to run single phase equipment, that I can assemble a power distribution box to split out single phase from the 208v 3phase. Again, taking 8/5 cable and a male 5pin connector to plug into that 208v 3phase, then running that to a box and splitting it to power 50amp 240v 3prong plugs. Using 2phases of the 3phase power should give me single phase 208v. Using just one to neutral should give me 120v single phase. (Here's where I suspect that I don't fully understand).
I'm old enough and experienced enough to understand that absolute ignorance generally won't kill you. What kills you is when what you think you know isn't actually correct.
I notice that almost all 3phase industrial equipment is directly wired. This leads me to believe that plugging it in may be a hazardous activity, prone to arcing. To offset this, I would only connect or disconnect while the genset is off.
Please don't respond with a suggestion that I hire a professional. The primary purpose isn't to get this completed. The primary purpose is to learn and have fun. Any and all risk is fully my responsibility.
Edit - looks like I'm trying to reinvent the wheel. Picture added of a box that does pretty much exactly what I'm trying to do.