I just got my nova a week ago and I think its pretty sweet. Not sure if all info is correct but here goes.
1. in program (basic) one, the choices are low, band, and highpass-at 12 18 and 24db. In performance(multi) you get a filter for each voice(6 total).
2. not sure?
3. No, but the general design of this synth means that there is a dedicated knob or button for EACH and EVERY function. A nice feature.
4. fx: there are six different buttons on the fx section and each is for a different type of effect. I think you get one effect from each type. And really there is not that much to the algorythms. Distortion is not very strong, chorus flanger and phaser all sound quite symilar. And really the fx are there for widening the sounds till they fit right in the mix.
A few more thoughts. The overall sound is great, and VERY LARGE! Presets are pretty good with a lot of nostalgic patches that are right on the money. Excellent real time control, and ABSOLUTELY EVERY button and knob transmit midi! The selling point for me was that it sounds exactly the same in multi as in single mode.
Maybe wait till the new nova2 and Supernova 2 come out and you might see price reductions !