I just finished my RAI and started my Levothyoxin at 150mcg once a day as ordered by my endocrinologist. I think you'll probably have more contact with your endo in the future, so I'd follow his/her instructions. Just watch for feeling anxious or flushed, or feeling all "revved up." If you do, then call the endo to adjust your dosage.
Lots of people here who have been down the road before us to answer questions. I'm certainly glad I found this website.