Wow. I hate to say it, but you may have just bought a big headache.
1) Where are the oil leaks? Head? Valve cover? Oil pan? The last two are easily (and cheaply) replaced. Head? You have other issues if that is the case.
2) Are you losing coolent?
3) Have you checked to make sure your catalytic converter is not plugged up? An exhaust shop can tell you pretty quickly, and most will check for nothing (or a very small fee). If it is plugged up, it will start to cause your O2 sensors to foul out. The back pressure will also foul out everything else quickly - I found out from personal experience on this one.
4) rattling engine - top end or bottom end? Use a mechanics scope to figure that out.
Top end means that you may need to replace some valve lash shims (DOHC) or replace some rockers (SOHC) if it is excessive. You may even need to replace some valve springs if they are not within spec. Most cars rattle some, but when you can hear it rattle over the radio, it is well into the excessive range.... My engine only rattles when cold and then gets quiet. If it don't get quiet after warmup, you may be getting close to excessive wear.
Bottom end means you have some real problems - most likely bad bearings and rotten oil pressure too.
Do a quick engine compression check (valid range should be 175 - 185psi) with no cylinder more then 10% from the others. Service life is 155psi at which point it is time to rebuild.
You should also do a quick leak down check to see if your valves all seal up properly.
Doing an oil pressure check is a PITA, but if you do it, you can really get an idea if your car is going to hold up bearing wise, because poor oil pressure will kill your engine quicker then anything else.