My van is overheating.

My van has multiple problems. It is a 2000 Chevy Venture, 130910-mileage. First there is a noise, that sounds like the power steering pump. On further inspection someone told us that it was the alternator pulley. Recently it started overheating, and the low coolant light came on. We filled it with coolant, and still overheating. Then the water pump went out, replaced it right away. Now we have water in the oil. When driving a short distance it starts wanting to stop, and when it does, it doesn't start. I have to wait for awhile, then it starts back up. I haven't had it checked by a mechanic yet. I was wondering what it could be? I don't know anything about cars. I will be taking it to a mechanic shop soon. Just wanted to know ahead of time what the could be wrong with my van.