Calling prior to the reporting point sounds like a giant leap forward to me. I could never figure out why we need to call 10 miles out from a CTAF, yet we put aircraft at a precisely defined point and altitude inbound to the busiest airports with no prior call at all! It amazes me that there haven't been more collisions at GAAP reporting points.
As far as 6 aircraft in the circuit goes, the simplest way may be to require the next aircraft to do a full stop and taxi back when someone calls inbound if the circuit is full (and require a full stop from the inbound aircraft).
The general principle should be to give priority to aircraft that will only be in the circuit for a short time.