5 pounds is enough to make about 1.5 to 2 gallons of good cherry flavored beer. If you use them in 5 whole gallons of beer, the result will be pretty weak, just sort of pink and tart but not much else. You need to use a ton of cherries to get much flavor out of them.
No need to cook them. Freeze them, pits and all. Don't remove the pits as they add a lot of flavor. They do contain cyanide, but I've never heard of it killing anyone from putting them into a cherry flavored beer. The act of freezing the cherries helps pop open all the cell walls and release the flavors better. Then thaw them out, and rack your beer onto them in secondary, and allow to ferment a few more weeks. They'll add some serious tartness, as well as color, in addition to the flavor and aroma obviously. Good base beers... well, pretty much anything without a lot of hops.