1. I have not done it, but many have. Brian Enos Open Gun forum
and Brian Enos 9 major reloading thread
2. According to STI:
Q. I do not reload but want to shoot major power loads in your pistols. Where can I purchase 9mm and 38 super major loaded ammunition?
A. Atlanta Arms & Ammo. produces high quality ammunition for use in competition pistols. Their information is as follows. Atlanta Arms & Ammo. 721 Vine Cr. Social Circle, GA 30025 Phone:770-464-2203
And Atlanta Arms
got their own headstamp ".355 super" to make it harder to accidently stuff a 9 major into a gun not designed for it.
3. 9x23 is 9x23 Winchester. It is closer to 9x19 but stretched an extra 4mm. By the way, there is also "38 super comp" which I believe is 38 super but fully rimless.
4. The STI factory guns' SRP is $2700-3400, although used ones can be found in the market for less. Not sure how much an SVI is, brand new.