Definitely a handball to me, we got away with one. But then I think there was also a handball on Stoke earlier that should have been called. Not nearly as blatant, but probably still could have been a PK as I believe it was in the box.
N'Zonzi's red card was correct in my opinion. He was late, really had no chance on the ball and to me looked clearly like he was stamping on the player. He missed though, perhaps because he realized what he was doing at the very last second. But the intent was there. He kind of stepped over the player to do it, it was not at all a natural tackling motion.
Clattenberg definitely blew a series of calls near the end that went Saints' way. But overall, I don't think it mattered. Jerome's strike was fantastic, but also a bit lucky so in a certain sense "undeserved." But you did dominate the second half. OTOH you were also rather bad the first half so really can't complain about being down 3-1 especially when two of the goals you practically put in your own net.
Think a draw was probably a fair result, though the score and the way it happened was quite remarkable. Very entertaining match.