I talk a little about the conversion I did on a Lightweight Commander here.
http://www.thehighroad.org/showthread.php?t=234282
I would NOT recommend starting the project the way I did. I began with a .45 LW Commander because I found one unaltered for less than $600.00. I couldn't touch a stock LW Commander in 9mm or 38 Super for less than $1,000.
I use Metalform 38 Super mags for everything in this gun. 9x23, 38 Super, 9mm. They all run. I do have some of the different variations of mags using the spacers, both back spacers and the front "crease" mags. I don't see a difference in performance at all between those 9mm dedicated mags and the 38 Super length mags.
I'd go with a 1911 unless you have ogre-sized hands. Double column guns for these long cartridges are not for those with small hands. And the single column guns carry much better because they're slimmer. If it's a range gun, or a fun gun, that might not be a concern.
If you do go with a double column gun, go the STI route. I'm not convinced the Para frames have the quality I demand when investing that sort of money into a gun.
Keep the original 9mm barrel. One of the big bonuses of a 9x23 conversion is the ease of dropping the 9mm barrel in for practice. If you ream your 9mm chamber out, you'll have to have another barrel fit. Why pay for work twice? Buy it once.
When Jim Garthwaite builds 9x23 guns he often buys a 9mm barrel and reams it out, fits it, and then it's good to go.
Some folks find they can use their 38 Super barrel for 9x23 with no problem. The extractor is rarely an issue, unless its a piece of crap or some proprietary sort of extractor.
The simplest, and cheapest way to do it is on a standard 1911 platform, or go STI.
Use anything else, and you'll be plagued with problems finding replacement parts. Parts break, spring going sproing, and you'll want another magazine or two someday.
Don't try to reinvent the wheel. Don't overthink it. The STI platforms, and those who use the 1911 platform to build 9x23 projects, have all the bugaboos worked out already. Unless you have deep pockets, or are a relative of a gunsmith the caliber of Jim Garthwaite or Dane Burns, go with the industry standard. You'll enjoy the gun a lot more over its lifetime.