Usually when College Board grants accomodations for the PSAT, they grant it for all of their tests at the same time (PSAT, SAT, SAT Subject Tests, and AP). You do need to register early if you need accomodations (like extra time), not all locations offer them. Another reason to lay out the testing calendar early for the OP.

I do not think any colleges express a preference for the ACT vs. the SAT. Almost every college takes both. And I think there is only one college left (maybe Georgetown?) that wants 3 subject tests -- all the rest take 2 now (since writing was added to the SAT & ACT). So whatever your kid is best at will be accepted anywhere.