Morning Jerry
All straight forward stuff, even easier if you have access to a lift. If not the get the car as high as possible and well supported on axel stands. Gearbox I use ZF parts and Longlife fluid last service parts Fluid Filter gaskets etc cost £250 as a kit (Tip make sure you can undo the filler plug first) If your car has Dynamic Drive rear diff it will nave 3 compartments requiring 2 different oils 2 outer chambers use a Carbon Modified SAE 75 80 oil (i buy from BMW it comes in measured .5ltr bottles) the main Diff section uses a standard 75 90 (I use Liquid Moly) same tip make sure you can undo the filler plugs first I know two people who drained the diff and couldn't move the filler plug !!
Front Diff Oil and Transfer case fluid I buy from BMW, the transfer case drain plug is a Faff to get to BMW drop the Transfer case support frame, I brought a stubby Hex drive set so I could get at it
If you have INPA/ISTA there are Workshop directions and guides
Good luck
Dave