Okay, here's an update!
I left a message for my endo regarding beta blocker, splitting my Methimazole 10mg in half to take 1/2 twice daily in am and bedtime, and exercising.I explained that I found a support group and had research a lot about GD and these questions had come up. He called me back a couple hours later!
I was very happy that he thought exercising as I'm doing is fine, I can split the Methimazole in half, and he prescribed Atenolol 25mg for me to take to relieve the rapid heartbeat I've been having. I asked my pharmacist if I can split the Atenolol in half to start with, and she said that was fine. I'm having enough weird things going on with my body I didn't want to throw something extra full blast at it. I'm going to try with the half pill twice a day of Methimazole for a few days before I try the Atenolol. Then I'll start with half a 25mg pill for a few days and go from there.
Thank you all so much for providing me with ideas, information and support while I figure things out!
This makes me feel like I have a bit of control over my treatment. Thank you, thank you, thank you!