1. DVI-I carries bothe digital and analog signals, so you could use a DVI-to-VGA adapter to mate with an old monitor.http://www.differencebetween.net/technology/difference-between-dvi-i-and-dvi-d/
2. AFAIK, mini-HDMI has the same pinout as HDMI.
3. Either will work.
4. Dunno. There are sometimes strange issues that result over split connections as HDMI tries to negotiate a common resolution supported by both monitors.
Displayport is ATI, don't expect nVidia to help out any more than folks helped Sony with Betamax. By also dropping VGA - which few should be using by now and can be run off a DVI-I connector anyhow - there's more room to exhaust hot air out of the case.