Request for 98 Sunfire advice.

So I picked up a 98 Sunfire, 2.2L, automatic for $800. The body is in great shape but the engine is extremely dirty and it has a few small problems. The handbrake doesn't work and when I'm idling the oil light comes on. I'm going to replace the oil pressure switch and make sure that the oil pump screen isn't clogged. So my question is how hard would it be to replace the oil pump if it came to that? Also I read that worn bearings might cause low oil pressure also. So how hard would that be? And lastly any advice to cleaning off the engine? I want to make sure that I don't break anything when I do. Any help or advice you could offer would be very appreciated.

Thanks.