yes and yes.
skimmers help remove protein buildup and will help in algae and other nasty water issues in the tank. once you see one working and pulling stuff out of the water you will deffinately agree that its a good thing to have no matter what size tank you have.
the powerhead keeps the water moving you want a target of 10 times the tank volume per hour and try to eliminate dead spots in the tank so I would go for about 3-4 smaller powerheads instead of one larger one.
Mike