Hi,
Your primary thyroid hormones are T4 and to a lesser extent T3. They're best measured in their free form with free T4 (FT4) and FT3 levels. You have what's called T3 thyrotoxicosis in that your FT4 is normal and T3 is elevated. About 30% of Graves' patients have this. Since we have about 8 times as much FT4 as FT3, your thyroid status is usually based on your FT4 level. So you'd be said to have mild hyperthyroidism with T3 thyrotoxicosis.
The usual starting dose of mmi is 20 mg. You're on a lower dose to help prevent FT4 from falling too much. Since FT3 takes longer to fall than FT4, labs in 2 weeks will give a good idea if your FT4 is falling too much and by then FT3 should be close to being within range.
Your TSI is high, but you probably also have blocking TSH receptor antibodies that are preventing TSI from causing more severe hyperthyroidism. The TSI result confirms your diagnosis of GD and won't need to be rechecked anytime soon. The pituitary hormone TSH will stay low for a long time---while on meds, a low TSH doesn't mean that you're still hyperthyroid. Best, Elaine