Having a big refugium will help system stability a lot and will act as a great filter for your main system. I have been running a 40g tank with a 40g refugium for 4 years now. The system is skimmerless AND gets virually no water changes (maybe two a year).
Now, I havn't pushed the system much to see what the refugium/filter can handle. I have 4 seahorses and 1 bangai. I have had a chilli coral and a few discosoma shrooms in the tank for most of the 4 years and recently added two small gorgonians.
In the early stages I had to dose nitrates regularly and even dosed phosphate a couple of times to keep the macro from crashing. It now seems pretty stable. Nitrates ran between undetectable and 5ppm and phosphates between undetectable and .2ppm back when I measured.
My refugium and tank produce enough zooplankton that I have had a seahorse develop and grow from fry to adulthood without my help. To this day he feeds on nothing but the amphipods and copepods in the system.
I do not think that my system has more diversity than other tanks out there, but it does seem to have a higher density of those creatures that are in the system.
As for recycling the water, doubtful plan at best.
It has been written many times and I will repeat... There's more than one way to fillet a fish and they can all work equally well... if you have an open mind.
There have been some very good discussions here on skimmerless tanks. Do a search and do some reading there.
There is also a very good thread on skimmerless tanks in Eric Bornemans forum over at Marine Depot.
If you have any more questions, ask away and I will answer as best as I can.
Fred