what size of bar is good for a chainsaw?
I am looking to buy my first chainsaw to use for sectioning fallen trees some 20" inches in diameter. I don't want to spend too much in case I screw up the saw; however, I don't want a piece of crap. What do you suggest?

Ask someone from the place you bought it from. They would be able to tell you what you need to use for certain things. Sometimes you need a smaller one, sometimes you need a big huge one.