Hi Michael,,,Welcome to the board!
Personally I don't care for brakes on hunting rigs,,,but that's pretty much a personal choice. They do help manage recoil however.
The 45-70 is a brute without question, and would be one I would consider porting or braking. The one I had did have 4 magna ports, and still was more than I really cared for. Brakes are generally more effective, but I can't say about the muzzle tamer, as I haven't shot one. The 30-30 will be much more pleasant to shoot, even without any recoil reduction of sorts. I would invest in a good fitting grip first.
Handloading is the best way to utilize the potential of these type of handguns, but the 30-30 will make for a good deer round with factory ammo, so long as you use it within it's limitations. The lighter weights like the 150gr. would be good. I hear of some using lighter bullet weights with good results.
Single shots really aren't a disadvantage, just hunt a little closer and make the first shot count. They do however present a different challenge.
Dave