Get the biggest pot you can afford, for a 5 gallon batch, full boil, I would go with at least an 8 gallon (32qt) or even a 10 gallon. With a 10 gallon pot and a voile curtain bag, you can move up to all grain batches with little to no extra expense using BIAB.
Draft 1: Lightly smoked Weizen
Draft 2: Belgian Wit
Draft 3: Rauchbier
Primary 1: German Scwarzbier
On Deck: Belgian Brown Ale, Pale Ale, Stout