OK, I need me some wheel learnin'....

I currently have two sets of steel rims that have been beat to heck and back and one set of no-name aluminum rims. At the end of last season I began thinking about picking up a set (6 rims, actually) of Panasports because, well, I dunno I guess just because I heard they were the bee's knees. However, now we are expecting our first wee one and so I need to be extra sure that I am spending every race dollar responsibly.

So my questions are:
1) Are aftermarket "street" rims acceptable for IT racing, or should I only shop for dedicated race rims that have been designed with the purpose of being stressed on the track?
2) What are the differences between street and race rims?
3) Out of pure curiosity, why does Panasport have the following disclaimer for their race rims "Panasport Racing Wheels are for RACING PURPOSES ONLY, not for street or highway use." I would think that if they're good enough for the track they would be fine for public roads, or are there certain tests that street legal rims have to pass that race rims are not subject to?
4) Should I even bother trading out my current rims? The only real reason I'm concerned with them is that they are an unknown, I don't know how long they've been in service and such.
5) Lastly, where can I find hub rings (or whatever they're called), my aluminum rims are not hub centric and I know there are little ring adapters you can get, I just haven't found a place that carries them.

Thanks for your knowledge!