I would personally separate out these issues:

- Vacuum leaks are extremely common on these cars due to the age and the vacuum lines and associated parts getting brittle. I don't see that as related to any of your other problems. You need to get a vacuum pump on each of the lines, usually to first isolate whether the problem is under the hood or in the cabin and if is is in the cabin, then to isolate each line to figure out which vacuum actuator it is. If it is inside, it is most likely a vacuum actuator on one of the doors.

- The oil leaks are pretty common and require a bit of work to deal with. Some people let the minor ones go for a long time and it isn't a problem as long as you keep enough oil in the crankcase. I always check mine when I fill up for fuel. When you diagnose it, there's tons of info here on what to do for each one.

- The injectors are most likely the cause of shaking at idle. Some shaking is normal as it is a diesel, but most likely you have fuel carbon build-ups inside the injectors and they need to be either cleaned or rebuilt with new nozzles. Diesel purge may help as may an Italian tune-up, but often the injectors just need to be pulled out and cleaned. I believe the maintenance interval is every 100,000 miles but it may be sooner for you due to the number of years and it may be more of an issue if the car has been sitting for a long period of time. I've started adding WalMart 2-stroke oil (1 oz per fuel fillup) and it has helped with idle shaking -- gone from minimal to rarely ever noticeable. Mach4 has a thread on it here somewhere.

- For the smoking, if it is the valve stem seals you will notice it getting rapidly worse over time to the point where it is smoking at idle and then pretty much all the time. I don't believe the issue is mechanically catastrophic, but you will get tired of it pretty quickly.

Dkr.