Coupla quick answers to your questions, coming to you all the way from Plano.
1) You are checking the a/t fluid with the engine running, right? It's supposed to be done with engine idling, trans in park, and fluid completely warmed up - as in 15 minutes of highway driving. It will read well above full if checked with the engine off.
Best way to remove excess fluid is using a suction device with a tube down the filler. A topside oil changer works nicely, but there are probably other options.
2) I've always used synthetic diff oil in all my MBs, never a problem. I use Mobil 1, but other products should be just fine too. Easy to change, just get the correct size allen head socket (14mm, I think...) and be sure you break the upper fill plug loose before removing the lower fill plug.
3) A special ball joint press is required to install the new ball joints. Your best strategy is probably to remove the lower control arms from the car and take them to a machine shop to have the replacement ball joints pressed in. Of course, the shop manual says you need a spring compressor to disassemble the front suspension.
Best manual is the official MB 124 chassis manual. About $125 directly from MB - I think they also sell it at this site? Two CDs, about 1gig of information. Some folks have complained about the organization of the manual, but I find it's something you come to understand over time. Lots of information.