Your body naturally produces 25mcg daily. Starting there will suppress natural production for no increase in metabolism. Most pills come in 50mcg doses, so I’d say start there.
Just remember the thyroid can be a bitch to manage. There’s no significant data I can find that shows T3 use leads to lifelong suppression, but if you don’t wean down appropriately you will feel like death (ask dirt). Be sure if you get labs drawn by your physician they know you’re supplementing T3 or else they will freak out about your labs.
It’s a serious compound. Treat it accordingly.