Fluids for Oil/Trans/FD change

[Armo]

I got a 12k mile maintenance kit from http://www.beemerboneyard.com/ and it came with plugs, o-rings, and crush rings to change out the Oil, Transmission fluid, and Final Drive fluid.

my questions are:

what type of oil: normal/synthetic should i use
what weight of oil should i use
and is there anything i should look out for when i perform the maintenance?

i read the FAQ on changing the fluids and it seems pretty straight forward. i just need to wait for my oil filter wrench to come in.

[boxermania]

Engine - 20 W 50 dino or 20 W 50 Synthetic
Trany and rear end - 75 W 90