There is not a code requirement to have a disconnect at the transformer. The transformer primary does require an OCPD, but that can be at the main gear and provide the required protection for both the feeder conductors and the primary side of the transformer. As for your isolated grounds look at 250.146(D). They must trerminate at a point where they can clear any ground fault. For your SDS, that would be at the same point where you connect the grounding electrode conductor for the secondary of the transformer.
[This message has been edited by resqcapt19 (edited 06-10-2002).]