-Was Mint overkill with Amb? It streamlined my deck, but left my Amb pretty useless.
Yes, Mint was overkill. At that point your deck really wanted a Stables.
In general, ambassador loves cards that draw other cards and give actions (Caravan, Laboratory, Stables).
If you get to the point where you can ambassador two useless cards *and* buy something usefull, you're in business.
Plus as the (correct) copper buy suggests, you couldn't afford Mint at the time.
-Did I actually want Jester? It could've done better, but...eh.
Jester is off course a good card in a deck that still needs buying power. However, you're low on +actions/high on terminals already.
And also...
-Skipping Sea Hag was a good idea, right? Or would've been if he had picked up an Amb?
... I would have wanted a Sea Hag in stead of it. You opened with Ambassador, he didn't. You made the better decision there. You are probably going to win this game. But what you can be absolutely 100% about is that you're going to win this *if it turns into being a very long game*. Sea Hag is a serious power card for slowing down your opponent. Not only does it give a curse, it also puts it in his next hand. Lookout/Native village make it slightly weaker but still strong.
(skipping sea hag on opening is a good plan btw, exactly for the reasons you mentioned).
-How about Stables? I don't think I wanted it, since I had few crappy treasures or spammable actions I wanted to cycle.
As I said before, I think you should want it. I'd try to turn my deck into something that has 1 ambassador and 1 sea hag, and then manages to play both every single turn. (2 ambassadors is an alternative). Play them on and on and on and on, until the point your opponent just pukes some mix of coppers, estates and/or curses.
-What do you do with Tournament wins here? I go for Followers over Trusty Steed about 2/3 of the time, but I'm not sure this should've been one of the exceptions.
I go for followers more often, and I think you made the right pick here.