Glenn,
You are to be commended for giving this issue some thought and for putting together some considerations.
Just a couple of points to address so as not to create any misconceptions.
I am assuming your intention is for these considerations to be used by General Aviation aircraft and students and/or low time pilots. General Aviation aircraft that fall within this area are no more than 1000 to 1300kgs in MTOW.
Vref is a function of weight. In the aircraft assumed to be operated and these considerations used is nebulas as it does not change due to the relative small amounts in weight variation. Manufacturers generally quote an initial and final approach speed in the aircrafts POH. In the aircraft concerned, this would be anywhere from 55 to 70kts IAS.
Hence, to quote of Vref + 20 could give a false impression of being "stable". POH annotated final approach speed of 60kts with a 20kt additive is just "not quite right" for conforming to being stable.
Like wise with your quoted 1000'/min sink rate. Sink rate is a function of speed which is in turn, a function of weight. To illiterate this, a B777's stable approach has a sink rate of 800'/min with a Landing Weight of 200,000kgs has a Vref + 5 speed of approximately 135kts IAS. 3 degree glide path at 135kts gives 800'/min. 135kts is the average cruise speed of you GA retractable under carriage and Constant Speed Propller aircraft. Get my point?
May I suggest that emphasis be directed to a more disciplined approach to flying circuits and closer adhearence to those "cues" that were thought in basic flying training. For instance, maintaining the "aim point" using piloting skills and use of changes in power in conjunction with slight changes in pitch.
If, as you say, you head that operation, then some basic airmanship requirements need to be put into your Operations Manual. For example: minimum height AGL to be aligned with runway center line and minimum height AGL to be configured and on POH annotated final approach speed by day and by night listing minimum visibility for both.
Just my two cents......