Engine Trouble? help?

I looked at a 1997 Honda Prelude with 150K miles and everything seemed to check out just fine. The only things that worried me were that first off, the power steering fluid was low. Is that normal for cars to eventually run low or does that mean that there is a leak? (the power steering pump was just replaced not too long ago). Another thing is that is had a little bit of oil under the oil pan but the guy said he uses 5w-30 oil in it and so could it just be that he is running too thin of an oil for a car with 150k miles? And lastly when you would accelerate and then come to a stop the engine would shudder for a second or two when stopped. What would cause the engine to shudder for a second or two when its at idle after acceleration? (the rpms drop below idle and then goes back to normal)