RE: Getting Started
What is your budget? You can get a big boat (like 40-55") that runs on regular gas with a run times over 30 minutes at 30-40 mph for $1000+. You can also get a smaller nitro boat anywhere from $250 on up and run 30 mph but with shorter run times.
Without R/C exerience I suggest an assembled boat of your liking where you add the radio equipment. You might want to try electric boats first to get your feet wet (so to speak) :-) Electrics are easier to deal with and can go plenty fast.
Keep it simple for your first boat and you will have a lot of fun!!
Post more questions if you have them.