I recently purchased a '95 E320 wagon with 59,000 miles on it. Runs like a champ but:

1) I think the rear end is sagging. Still a good 2" between the top of the wheel and the wheel well lip. Have not found any info regarding the OEM specs for this.
2) The car is on its second set of tires. The two rear tires needed to be replaced while the fronts are fine. I think this is due to the the suspension issues which have generated excess wear?
3) From what I've read here, the rear subframe mounts probably need to be changed. Do I have to do all three or is the differential mount more problematic and replacing this alone likely to solve my problem?
4) What does the above operation require in man hours and parts (I'll take the man hours and multiply it by the rate at the shop I take the car to in order to get a good estimate).
5) The ride is typical Mercedes except when I go over bumps. Then it gets very harsh. I think this is just inherent with wagons. But will changing the differential/subframe mounts make a big difference?
6) *BONUS* question. The car came shod with "Embassy" brand tires. Are they any good? Never heard of them. When I changed out the rear tires to Michelin, the ride improved dramatically. If Embassy is an off-brand, I'll chuck the fronts and replace with Michelins. Also, is it difficult to mount the balancing weights on the inside of the rim rather than the outside? (Would like to know before the tire guys laugh at me).

Thank you in advance for your assistance!