Julie,
AIP ENR 1.20.2, or for the online version click on the 'Approach Procedures, Use of Navaids' in the Index.
What you have said is correct, except that descent to the approach MDA after the initial fix is allowed only if no other altitude requirement exists - which they usually do in a comman reversal procedure for an NDB or VOR approach, with descent to the final MDA allowed once established inbound.