Very nice! Love the gold snowflakes. If you do some digging, you may be able to find some '82-'83 bumpers, which are smoother and paint-matched.
The '81 has a few unique parts such as the distributor that do not cross to other models - keep that in mind when parts shopping or troubleshooting. For the '81 you need the '79-'81 FSM and an additional smaller '81 "Turbo Supplement" manual.
Big rust areas are the front frame rails which are just there to strengthen the floors. People tend to use them as jack points and crush them. Also check the spare tire well.
I'd still use a modern A3/B4 such as Mobil 1 0W-40. A 5W-40 HDEO like Rotella T6 would also suit you well. An High Mileage oil isn't needed - you don't have an High Mileage engine!
Enjoy the car, and ignore negative comments regarding the transmission - it was the only option in '81, and with a shift kit it'll really hit the gears!
FWIW, you can safely run 10 psi on the stock engine management with NO danger - really wakes the car up with an additional ~50hp!