There's about a dozen different things that can cause rough idle on these cars, including motor mounts. There's an awful lot of stuff on 400E rough idle in the archives (search). Are you getting any fault codes? Building a code tester (also in the archives) is a good first step.

The oil pressure issue is almost certainly the sending unit which is located at the base of the oil filter housing. It's not too tough to replace, accessible from the bottom, and not too expensive, maybe $40.

Could be warped rotors - these cars have a history of being pretty hard on brakes.