I have an 11gal pot and its perfect. I never worry about boil overs so the boil is pretty much set and forget. I would say that that about 11 should be the minimum gives the ability to do some high gravity bress as well.
primaries: BRown Ale
secondaries: Rye IPA
Bottled: IPA, Pigs ear brown clone, stovepipe porter, German Alt, Oktober fest ale, Smoked IPA, failed pale ale, 1st AG ESB, belgian wit, Ipa#2, , Lake wheat, fish Red ale, Smoked wheat,
KEGS: blonde Nugs , Sugar pale light, chin nook ale (gone in 1 week)