The short answer is yes, a 17 gal. livewell is large enough for a bass tourney. Remember though that your livewell is never full, it's usually half full. That makes it an 8.5 gal. livewell. If you're planning on fishing for other species, particularly esox, you'll need a long livewell.
Fishing tourneys is about the only reason anyone could need a livewell. I've disconnected mine and now use it for storing baits. I don't often keep fish so they get released right away. If I choose to keep some, the best method is to quickly dispatch them and put them on ice.