CAS has a number of different shooter classifications.
It boils down to what type of pistols(C&B or cartridge) you shoot and the way you shoot them(one vs. two handed hold) and choice of propellant(Holy black vs. smokeless).
Two revolvers are pretty much mandatory. Most shooting stages do not have a reload in the scenario. You could do it with a single gun but your times will be exceedingly long.
Lever guns in pistol calibers are pretty standard. It really helps to have the rifle in the same caliber as your pistols.
Caliber in rifle must be .25 or larger, pistol .32 or larger.
Shotgun must be .20ga are larger. You can use smaller gauges but you will not be allowed to win. You will be DQ'ed but can still shoot the stages.
Most folks are pretty cool about helping newbies. Just head to a shoot. Be cool and ask questions. Most folks will readily answer.
Unless you have an extremely thick wallet, reloading is almost mandatory.
You'll shoot about 100-150 pistol/rifle rounds each match. Shotgun about 20-50 rounds. Add in a few hundred practice rounds and you can see the cost.
Ammo velocity must be kept low to moderate. No super-duper reloads allowed. Cast lead bullets only. NO JACKETED AMMO.
Some of the ammo makers manufacter cowboy ammo just for CAS so it is low velocity.
The usual drill on a shooting stage is a mixture of shooting the pistols, rifle, and shotgun. Range distance is normally quite short like inside of 30yds
The big rifles like the Sharps, Rolling Blocks, Large frame Lever guns, etc are fired alone in a side match at longer distances up to several hundred yards.
In the larger shoots there are also side matches for pocket revolvers and even derringer type guns.
A real handy thing to have is a small wagon or cart to carry all your stuff. Some ranges require you to carry all your gear quite a distance from the vehicle. Toting 100pounds of gear can be a real pain.
Once you get to a match or two you'll have a much better idea of what types of equipment you'll need.
Best advice: Start slow. DOn't jump off into a boatload of expensive gear.
The gun bug in you will eat you alive wanting all the cool old guns.
If you want to start a MAJOR debate ask "Which guns are best"! LMAO
Ruger makes a darn good entry level gun in the Vaquero. It can also double as a heavy duty revolver on the range or field. The Colt SAA's and clones can't tolerate heavy loads.
Like any other shooting group you have a great difference in peoples attitude toward the hobby. Some are just weekend warriors who want to shoot and have fun. The there are the hard cores who are ate up with it. Most folks fall somewhere in between.
Start looking at various people of the Old West era. Decide what type of person you want to portray. The list is endless:gambler, cowboy, city dude, indian scout, soldier, etc. Pick one and start assembling your costume. The civil war re-enactor web sites will hook you up with the soldier stuff.
It really just depends on you as how far you want to go in costuming and period correctness.
Whew...I need a drink! LOL