Wow, so many questions in one post...surprised nobody even attempted to answer some of them. I'll try my best.
91 and 92 turbod cars are pretty much the same. Some changes were made halfway through 92, all of which are listed in the FAQ...so check that out.
As far as the price of rebuilds. Perhaps they are listed as more expensive, because either a) the owner will be paying somebody else to do the work, or b) the person giving the quote was suggesting aftermarket upgraded internals.
As far as the 2 companys/websites you mentioned, I have never heard of either, so I really couldn't fairly comment on either. Generally, the 3S community is pretty much a tight-knit group, so we try and keep our business with the companies that support our platform. Many companies overlook our cars due to the rarity and lack of continued production...so we generally support those companies who have made themselves a part of our community.
That said, cams can be found at
www.3sxperformance.com and
www.dynamicracing.com and possibly even
www.importpoweronline.com (not sure about that one) And probably a few other sites mentioned in the FAQ.
The stroker kits are being made by:
http://www.pampenamotorsports.com/
I don't honestly know whether the stroker kits are available yet...so I can't comment on the possible complications. But considering that they are coming from Ray's shop...I'd guess they will be top-quality. He has a vr4 with 700-800hp, and is an amazing tuner...so he knows what he is doing.
As far as how to reach 500hp...are you talking at the crank or at the wheels. Regardless, there are many ways to reach it...but you will need to do a turbo upgrade. There are dozens of options, which should all be researched. As many are good for track use and can produce really high hp numbers...but may not be the most practical for street use, due to the high-octane demands. It really comes down to a personal choice of what will meet your needs/desires. If you check out
www.3si.org/forum There are hundreds of threads comparing a variety of turbo upgrades. Some of the more popular ones are the DR500s, DR650s, 13Gs, 15Gs, 13Ts. These are the ones primarily used on the street. DR800s, DR1000s, 17Gs, 20Gs, etc are more track-specific turbos IMO...but obviously there are people who mix that analysis up and have their own opinoins...so please don't take that as anything more than my opinion.
There are some upgrade guides in the FAQ as well that you may wish to check out.
Also, check out
www.stealth316.com I don't know if you are familiar with this site, but it has TONS of invaluable information relevant to many different topics.
Bodykits will meet with varied opinions around here. There are those who like them, and those who despise them. But if you do a search, you can find most of those threads.
Lowering is an excellent idea for a variety of reasons. Obviously less air under the car, better cornering, less body roll, less ugly wheel gap, etc. I think
www.3sxperformance.com has the majority of good options available for our car. Obviously the other vendors may have better prices, so check them out as well.
Hope that helps. Also when you have a question, try doing a search as alot of this info has been discussed previously.