I've been diving for about 5 years, so I'll try to give you some advice. First off, where to buy the gear. I'm extremely fond of
www.scubatoys.com. Scuba Toys is an actual shop in Dallas, TX. I bought my first set of gear from a local shop, and have bought everything since then from ScubaToys. I've found that they have the best price (and if you find a better one, they match it). Also, if you are a member of their forums, or
www.scubaboard.com forums, you get 10% off....so basically they have the lowest price around, then take some more off. (no, I don't work for them, never have)
As for a knife....you aren't going to be stabbing anything. Ever. Your knife is to cut fishing line or rope that may entangle you. I've found the best tool for this is a pair of EMT shears (
http://scubatoys.com/store/detail.asp?PRODUCT_ID=KN25) They don't look half as cool as a big knife on your leg, but their functionality is perfect. If you do decide you want a real knife, go with something with a blunt tip. You often can't actually see the holster underwater, so making it harder to cut/stab yourself is good. Plus the square tip can be used for prying and whatnot. (
http://scubatoys.com/store/detail.asp?PRODUCT_ID=Oceanic_Titanium_Knife) Titanium is really nice if you get a knife...never have to worry about corrosion, which is a problem even with stainless steel.