Welcome to the madness, Frank. I've been in your position for a while and have only recently pulled the trigger. You'll find a lot of useful information on this site so I'll recommend doing a search or just some free-form digging through past threads. However, I'll summarize what I found as long as you're aware of the caveat this this will be one person's opinion.
- Pan vs tube frame: The subject of many a religious war, there are several historical threads about this. I think the conclusion is that while many tube frames offer some engineering benefits, under normal use most folks won't be able to tell the difference in most instances as long as the pan frame was done properly. Tube frames do offer a slightly roomier interior.
- IRS vs swing-axle: Again, a lot of discussions on this. The concensus is that - all other factors being equal - IRS is the way to go BUT a swing axle can handle well and has the benefit of simplicity and commonality. A swing axle car will need a camber compensator ($65) and maybe a front sway bar.
- Wide-5 wheels and discs: Yes, it can be done.
- Fit and finish: Here's where I'll offer blatant opinions based on what I've seen in my research. Oh yeah, all price info I have is from websites and is for turn-key cars. For pure fit and finish, I'd say Intermeccanica (IM) and JPS Motorsports (JPS) are equal and at the top. IMs are built on a proprietary frame with quite a few advantages including roll-up windows, but they are quite a bit more expensive than the others - starting at over $30k. JPS is pan-based, although John Steele does offer a tube frame as an extra-cost option. His cars start in the low-mid $20s. The other major vendors are Special Editions (Beck, tube frame, upper 20's), Thunder Ranch (TR, partial tube frame utilizing a VW rear section for ease of titling, no price info), Vintage (VS, pan-based, low $20s), and Specialty Autoworks (SAW, mid-engined Subaru-powered and built in small quantities, not sure about prices). The pictures I've seen of the TR cars look great, but I've never seen one in the flesh, so I have no opinion on quality. There are several owners on this site. VS offers the lowest entry price and has the most owners - most of whom seem very happy with their cars. Those who have SAWs love 'em, and they are definitly the most modern mechanically. The one I saw in the flesh was beautifully made.
I am getting a Beck being built at the Carlisle, PA show and am about as excited as a kid at Christmas. I have enjoyed working with the vendor (Carey Hines at Special Editions) and expect the build-up to some serious fun. I like the 3" diameter DOM tube frame design, as well as a number of other features. You can private message me for more details.
Basically all of these are fun, so it comes down to the features you want and how much money you have. It'll be hard to go wrong. Oh yeah, I have a buddy with a new Solstice (he let me drive it - very nice!) who thinks these have a higher "coefficient of cool". I didn't look to see where you are located, but I STRONGLY recommend that you attend either Knott's Berry Farm show in LA in April, or the Carlisle, PA show in May. These are the two largest shows in the US and most of the vendors will be at each. It'll give you a chance to compare them side by side. Good luck!