It's a great time. Most of the CAS shooters around here are not gamers, so I don't think that many really care too much where they end up in the standings. That's one reason I like it so much. For local matches, not everyone even dresses up (or down). Lots of shooters showed up in jeans and t-shirts (it was hot).
As per weapons. Cutoff is, generally speaking, around 1899. If it's an antique or a reporduction or fascimile of an antique it's generally legal.
Lever action rifles generally use handgun ammunition. That is no 30-30s are allowed. Typical examples would include 1894 Marlin, Winchester 94 (handgun calibers), Rossi 92, the Italian Henry copy and quite a few original Winchester 1873, 1876, 1886, 1892, 1894s, Marlin 1881,1887, Spencers, Whitneys, etc. Though at the local level, the Marlins, modern Winchesters, and the Rossi dominates.
Rifle caliber lever actions can be used in long-range rifle stages but more folks use period single-shots. I've got a rebuilt Rolling Block myself for that purpose. This is where the 30-30 would be used, if that's all you had.
As for shotguns, anything with an exposed hammer is generally okay. Also double-barrls without an ejector are legal. That would include 1887 and 1901 Winchesters (lever action), 1893 1897 etc Marlins, 1897 Winchesters (pump action), Rossi Coach Guns, Stevens 311 series, Stoeger Coach Guns (double barrels with and without external hammers) just to name a few of each style.
Handguns must be single action revolvers only. No double action (even if original such as Colt Lightening or Thunderer, Smith & Wesson double actions, etc) or autoloading pistols of any sort are allowed.
The only exception to these rules would be side matches that are weapon specific. Stages such as a Wild Bunch stage or a Black Jack Pershing vs. Pancho Villa stage(good for the Mauser).
I believe the caliber restriction is a minimum of .32 caliber. All ammunition must be lead, no jacketed bullets are allowed anywhere in any match that I've ever seen or heard of. In CAS there is no minimum velocity for ammunition but there is a maximum; for revolvers it is 1000 fps and for rifles it is 1400 fps.
Generally to shoot a full match requires a shotgun, (handgun caliber) rifle and two revolvers. Long range rifle knife throwing, tomahawk throws and derringer are usually side matches, independent of the main match.
If you don't have all the weapons necessary, it's usually no problem. At this last match we had three new shooters in our possee of 10 people. Four people shared one of the revolvers. I brought along an extra Super Blackhawk against just such an eventuality but they all prefered to shoot their friend's Colt. Every match I've been to there has been sharing of weapons. At my first match I borrowed a total stranger's shotgun. He just asked that I return it after the match. You can't get much friendlier than that.
All in all, go to a local match. They're a ball. The people are really laid back and easy going at these affairs, except when it comes to safety. This is the only shooting game where I've seen loading and unloading tables for every stage of every match. In local matches, the rest of the posse are usually your ROs, timers, etc. If you don't dress up or have all the gear necessary, chances are someone will help out.