Wait - if you started Friday, that means how many days of track time? WOW!
Well, from the sounds of it, it was a success (isolating problems being a good thing). Unfortunately, I have nothing to offer to help, beyond hearsay.
1. no info. Were you running the factory upper mounts? I know those are notoriously weak. I can't imagine how bad that would be w/ a race sprung car?
2. Yes. I've heard some of the local rx7 guys bitching about how fast the 325's are. You could always call Sunbelt <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/biggrin.gif" border="0" valign="absmiddle" alt='
'> (do you know what those guys are getting out of their ITS 240 motors?)
3. I've heard mixed reviews on replacement of the subframe bushings (mixed in a random way, not good/bad). Going solid is definately bad - unless you are a drifter or dragger (reduces wheel hop when tires are spinning). The replacement stories I've heard ranged from no difference to a more solid feel. People I trust had reviews that said replacment was noticeable only in power on, when the weight shifts rearward. The benefit is supposed to be a more linear feel (so that you can feel traction better) w/o being so rigid as to void the functionality of the design.
If you troll backwards for a post on subframe bushings, you will find one of our members (something like s15sr20detek6... I know it has s15, sr20det, and ek6) who recently installed the Nismo subframe bushings on an s14. He also has an rx7 ITS car, so he might be a good source of info. I think he did that job back in early april/late march-ish.