For the record, I think this is a game where vineyards just beat the pants off of a province strategy, but let's ignore vineyards for this analysis, since there are many more bread-and-butter dominion lessons to be learned here.
1. You're absolutely right that an early sea hag is essential - probably so essential that it should be bought even with a five two split.
2. (because we're ignoring vineyards) I agree that moat is not worth it here.
3. Trashing - forge vs. trade route. I think forge is not a good idea on this board. It's expensive, so you can't expect to get one till late. By the time it comes around, it's unlikely you'll have forge AND the ability to draw cards (with + actions) AND a fist full of bad cards. And if you draw forge with a bunch of good cards, you'll REALLY wish it were a gold. So trade route is the way to go; however:
4. Opening sea hag/trade route is a fatal mistake. The problem is that neither of these cards do anything for you on the turn that you play them; they both help you later. Your deck on turns three and four will thus be worse at buying cards than it was on turns one and two - and if your opponent plays a sea hag, it will be even weaker when you reshuffle! So an early silver seems crucial. Buy a trade route later - this has the added benefit of decreasing the chance of drawing trade route with four coppers (which is terrible).
5. (Again since we're ignoring vineyards). I agree with Davio that the village buys are a mistake in this game. If two of your five villages were courtyards and three were silvers, your purchasing power would be much greater and your risk of action conflict would not be much higher.
If we choose not to ignore vineyards, I would open sea hag, moat, afterwards buying (roughly in priority order) worker's villages, trade routes, and moats, shifting to courtyards as the curses run out, and picking up a potion or two roughly around the time the opponent's deck gets two golds.