Sorry for my slow reply. You are right about both of these issues:
(1) the freeze-out temperature is certainly k_B*T ~ (E_c - E_donor band) .
(2) The law of mass action is only valid when freeze-out can be neglected.
If you are very adventurous, you might try deriving a modified version of law of mass action which includes these additional dopant band orbitals. You would have to define a density of states with a few orbitals between the conduction band and valence band. Then fixing N, you could in principle solve for the chemical potential. However, I think this rapidly becomes an analytic mess!
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