There is so much information about the subject of insulating a crawl
space, i've done a lot of searching and have come up with the basic
ideas of what I need to do.

I have a crawl space, with attached basement (a small 3x5 opening).
The only way into the area is from a small outside door into the
basement.

I've gathered that I should be insulating the walls of my crawlspace,
laying down a protective barrier, and sealing everything off. I have
an airhandler/ductwork inside the crawlspace and a water heater in the
basement. Do I need to do anything else? should I be worried about the
air handler down in the crawl space?