Hi Dave,
Good to hear, FP's will happen with all vendors, it just depends on how fast they are fixed.
Comodo is pursuing 30 minute updates after reporting a fix on the forums here, so I'd say that's pretty fast

I'm not familiar enough with PrevX but if it's a bit like ThreatFire I'd say it's not needed next to each other.
If you switch D+ to ProActive and know how it behaves (i like paranoid mode) then nothing should happen.
If you use common sense on browsing etc of course, don't play with "patches" and "cracks" on your live system for instance

I like to run scan's once a week with stuff like MalwareBytes Anti-Malware or SuperAntispyware and Gmer and/or other rootkit scanners, then once a month with the Ultimate Boot CD for Windows and Avira that should do the trick, save as much log files as you can if you need "proof" if something should happen to your bank account.