Safety Gear Q: Short sleeve SFI T shirt ok?

The reason for adding the underwear to the single-layer suits is to create a sort of poor man's multilayer setup--with the short-sleeve underwear, you're skipping a fairly significant portion of that extra layering. So it's gotta be long-sleeve underwear...sorry!

We can wear whatever the heck we want under our 2 layer suits, right? I'm going to be buying some cool vests and the above mentioned shirts would be great to wear under the vests, essentially creating 3 layers of protection.

so wait. 3.7 says "Multilayer suits rated SFI 3.2/A5 or higher are highly recommended and may be worn without longjohns". would that mean we could go commando?

Commando, and I dare anyone to check....

Speaking of fit, should overclothes and underclothes fit snugly, or should they be looser so one can move about easier?

That's really a personal preference. Undergarments are generally snugger, while your suit is looser, but not so loose as to be catching on anything in the car. Unless you are having a suit custom fitted, which is an option for Pyrotect and many other mfgs, you are gonna have to deal with whatever the off the rack size is. My Pyrotect multi-layer Deluxe suit is a large and is snug in some places, but the legs and sleeves are right length so I suck it up (or in, actually). Once on the suit is quite comfortable.

Pyrotect's suit sizing chart:

lulz.  now i see how that could be misinterpreted.