1. No. You can’t since HQ clips are per se opposite to anything we call proxy. This is original media.
2. No. If you did you’d end up relinking all media files that went off-line. I can’t give you fool-proof advice given the fact that I know next to nothing about particulars of your project.
3. Yes. You can capture DV footage as ProRes Proxy Clip (you need to have aja or black magic installed) then recapture clips used in edit as HQ ProRes footage.
Anyways, don’t mess with resolution and/or frame-rate. Proxy means light bandwidth, i.e. bit-rate, all the rest is exactly the same. Otherwise you’ll get yourself into a storm of s–t.
Free-lance fcp editor in Moscow
http://www.mokaeff.com