There is only one plug on the rear diff. It's for both drain and fill. What I do is remove the spare tire, pull the drain plug and then jack the front of the car up. I use my pump to get what's left out of there. I then refill with redline 75w90.
The front diff has two plugs. I bought 3 quarts for front and rear and used about 1 3/4 quarts between the two. I definitely wouldn't pay a shop if you were able to change xfer case fluid.
For the cooling system it takes about 10 quarts so you need two gallons. Also not hard to flush...you just need about 4 gallons of distilled water and to find the block drain.