Mobil 1 and how much for 4x4

I have bought my son a 2003 4 wheel drive DC. I am going to change out the fluids. How much does each take, the front and rear differentials and the transfer case. As I understand it they all take the same oil. I was planning on using Mobile 1 synthetic, 75-90w. Does this sound correct? I used Royal Purple in my 2004 Prerunner rearend, but that was only about 3 quarts at $18.99 per. That is why I have decided to go with Mobile 1, it would get expensive doing the front dif and transfer case. Thanks for your thoughts.

 

See factory service manual sticky near the top of the 1st Gen section.

 

2.3, 2.6 (3.1 w/locker), 1.1 - respectively