Lee, those smoked turkey breasts are fully cooked, at least 140F internal. Correct?
Answer 1.
I find slow thawing preserves moisture in meat. I think you are short in your planned reheating time at 140F. If the breasts are 2-inches thick i’d give them about 3 hours to safely and thoroughly reheat.
Reheating from frozen will take more than 50% longer.
Answer 2.
Reheat whole to preserve moisture.
The way i have been cooking turkey, mostly thighs, is to brine them overnight, then smoke two hours, vacuum pack them and finish cooking SV as if they were raw. I generally avoid freezing pasteurized meat unless i want to hold them beyond a month or more. The results are uniquely superior to any other turkey meat i have experienced.