Hi ODF

I agree with cobalt dream. I think it is much easier to deal with ( mild ) distortion than seams. As long as it isn't too severe it shouldn't be a problem. You may want to make a test map with just a simple color fill with noise added in to see how severe the stretching is. Texture artist ( and Im not one of them Lol ) can compensate by making micro detail smaller in areas that stretch where if you have split areas there's not much you can do unless as you said you have the tools to paint on the model in realtime.

I really think you should connect the upper and lower body and especially on the face don't split the lip/chin. That would make mask control maps nearly impossible. Of course this is just my opinion. It's easy to suggest things but it takes a lot of skill to actually pull it off. I just think the way it's cut now ( particuarly the lip/chin cut ) will be less flexible. Again Im far from an expert on any of this just a suggestion but I would probably mark the seams something like in this pic.