I second Gunslinger's advice to hang out at a couple of shoots. Introduce yourself to the chapter president or rangemaster (the "Mayor" or the "Sheriff"). They'll make an announcement to the group, and there will be someone there who will be glad to share a gun or two with you at the next shoot. If you don't know who/where they are, call SASS and they will give you a phone number.
I have yet to get a straight answer from SASS regarding the issue of one revolver or two. Last time I looked, the only reference in the rule book to reloading on the clock was in regard to black powder guns, and all it said is, you may switch cylinders. To be frank, I've never seen anybody use just one revolver, but I don't think anybody would have a problem with it; you'd just burn a lot of time reloading on the clock.
Do Blackhawks have adjustable sights? If so, they are in the modern class. The Vaquero, with its notch sights, is in the traditional class. In my local group, more people shoot traditional than modern, but modern shooters aren't rare by any means, and everybody shoots the same courses. I believe you have to shoot modern if you have one of each.
A couple of years ago, an importer called Tri-Star announced that their manufacturer in Turkey was going to build a replica of the Arnold Schwarzenegger, T2-style lever action shotgun, with Winchester's blueprints and blessing, but it seems to have fizzled. I've shot with 3 chapters, and at least half the people in each had the exposed-hammer Winchester pump (1897?). I'm sure someone in your group can help you get a line on one. I don't know how much they might cost - I have a cheap "Brand X" side-by-side.
About the ammo - the bullets have to be all lead. No copper jackets, no gas checks, no copper plating. There are also limits on the muzzle velocity. Many of the big ammo manufacturers now load "cowboy" ammo ($$$), but any light load, like a .38 Special lead round nose, will work just fine. For the shotgun, any of the upland game, or dove & quail loads, are the ones to use.
Most important of all - Have fun!