From my experience, run first a job using say 5 states, but putting only first in wstate array (wstate(1)=1,-0). If you see states close to your ground state, they may affect your ground state and you should consider them by putting to the wstate array. However, geometry optimization for SA-CASSCF was discussed here. Do a search.
How it is related to the active space?
I afraid, there is no relationship.
>3. How to carry out geometry optimization for mcscf? As I understand the orbitals will change at each step of the search. But I can reorder/select them only at the initial configuration… How the correct active space is determined/maintained during geometry search?
Every next step during a geometry optimization uses orbitals from previous. With good starting geometry and the correct active space it should not be a problem.
>4. My system is oxidase, i.e. triplet. But if I am trying to set MULT=3 and NAOS=2 NBOS=0 it complains “NAOS.NE.NBOS IN DRT INPUT DOES NOT MAKE SENSE.” How to model the triplet then and why there is no sense?
relevant part of the output file would be very informative for this case.