Your antibodies will probably decrease your first year on thyroid replacement.
You will lose weight, 5 to 10 lbs of water weight will come off fast. I started Levothyroxine (generic synthroid) in Feb of this year and I've lost about 15lbs and hope to lose 15 more. (haven't been trying lately - we have halloween candy in the house
Six weeks after starting therapy they will retest your blood levels to see if any adjustments are necessary. All symptoms should resolve shortly there after. You'll need your thyroid levels rechecked yearly.
If your symptoms don't go away completely or new symptoms appear - that's where the importance of a dedicated, well educated and not-so-busy-that-they-can't-talk-to-you endocrinologist comes in.
Tweaking of hormone levels is common to address any lingering symptoms.