RE: What is cubic wing loading????
Cubic wing loading is an empirical "rule of thumb" with little theoretical basis, but it seems to work for comparison of similar model aircraft of different size.
Yes flaperons will reduce landing speed. I think your assumption of a 25% reduction is quite optimistic. Something on the order of 10% is more likely. Spoilerons won't reduce landing speed, but both will increase approach angle which will make landings a bit easier.