can you descend to the intitial minimum approach altitude prior to the IAF
... Depends what you mean by "Initial Minimum Approach Altitude". The Initial Approach Segment commences at the IAF and ends at the IF, before that, IMHO, you should be flying at the Sector Safe Altitude. Descent below that level before passing the IAF may not provide terrain clearance (hope this isn't another case of Intl Variance?)
Regarding other traffic... for our "on airfield" NDB the IAF/hold is, naturally, in the overhead. If I clear traffic to the IAF and out on the procedure I think I'm entitled to expect the pilot not to fly below the minimum holding level until beacon outbound?
Am I wrong?