Hi Brian,
If you want to track elements to the head it's going to help to have multiple markers. But it all depends on what exactly you'll be compositing in. If you just need to lock the position of the animated element to the 'head' then you'd be fine tracking just a single marker (as long as it's always visible).
If you plan on tracking scale and rotation too, it gets a little more complicated and you'll need multiple markers on the head.
To minimize green spill on white clothing you'd typically want to stay as far away from the greenscreen background as possible. And the lighting needs to be right. Usually I'll light the subject with some magenta gels and color correct the slight red cast out in post. But the slightly red-ish lighting will help reduce green spill on the subject. And definitely don't underexpose the subject. You want the whites to be significantly brighter than the green background - which will help separate them when you're keying. I'm not sure what you mean by 'black taping the inside of the shirt'.
If the camera is locked on a tripod you won't need tracking markers on the greenscreen and you'll be happier leaving them off since you'll need to garbage mask them all out.
Good luck,
Barend
Raamw3rk - digital storytelling and visual effects
