Fat grafts to the hands can be highly satisfying to erase the stigmata of aging. I have patients, including weight lifters, refrain from vigorous exercise and heavy hand use for 4-6 weeks after the procedure to insure good graft survival.
Fat grafting of hands is a very meticulous procedure and should be done by someone with knowledge of hand anatomy. Best area to place fat grafts is deep over deep fascia covering hand muscles. Placed in that area fat grafts will last longer and create most natural result. Injections in the skin or just bellow the skin as performed by many "injectors" without knowledge of hand anatomy may create problems like prolonged swelling, deformities and even require emergency surgery!
Revision of neck scar should be done in the course of secondary neck lift. Usually scar underneath the skin flap is not a problem for safe dissection and neck muscles tightening during secondary neck lift. A minimal removal of skin, placement of scar in the crease behind the ear, and skin closure without any tension will improve chances for good, hidden scar after neck lift revision. Good luck
I've done fat transfers to the hands for rejuvenation for many years; the duration of the improvement is impacted by lifting weight because the pressure from this activity is not on the fat but on the palms. Scarring at the incision line can be removed during a second facelift. The extent of scarring under the skin will depend on the technique and quality of the first surgery; rarely is it a problem.