A +1 on what Doc said on the "starter kits". You sound like if you want to get into it, you want a good pistol that will provide good service - again, a +1 to what has been said. I've shot Colt replicas and Remington replicas - in 36 and 44. The Remington that was mentioned is an excellent gun that will provide good service in the years to come and also provide you with a lot of enjoyment. I don't know if you are new to BP or not so will mention a few suppliers as well that you can google.
Track Of The Wolf - a great on-line catalog - they carry just about everything you need in accessories as well as guns and gun parts - some pistol, rifle and shotgun - I've dealt with them for years and they are good folks
Dixie Gun Works - been around a lot of years and they have a lot to offer in guns and accessories
A suggestion on accessories - you'll need some type of powder container and probably one of the best things for shooting pistols would be to get a flask - there are a variety of styles out there
Powder measure - for starting out, a good adjustable measure that will allow you to measure a variety of load sizes until you find out what works best for you - there are some good brass ones out there
Percussion Caps - size will depend on the pistol you buy and what they recommend - whatever pistol you get, somebody on here will probably have one like it and can be of help in advising you on load sizes, ball sizes, cap sizes, etc.
Balls - the manual with the pistol you get will probably recommend a size or you can ask on here - depends on caliber, etc. "swaged balls" can be purchased in boxes of 100 - after a while, if you are so inclined, you may want to get into casting your own
Powder - you'll be using either real Black Powder or a substitute - depends on what you have available locally
Cleaning kit - these pistols create a lot of "foouling" - hot soapy water works good to clean with - if you don't get it cleaned good, what fouling is left can easily cause rust - I'd recommend a pistol cleaning kit of some sort that has a bore brush as well as a jag (most kits do) that will fit the caliber of your pistol and cleaning patches - store bought or home made from one of your better half's finest sheets!?
Some type of oil or other rust preventative to oil it down after you clean it - everybody has their favorite - WD40, gunoil, etc. - I use pure virgin olive oil most of the time
Lube - some type to cover the balls in the chamber after you've seated the ball in the cylinder - some have their own formula - Crisco works well to start with - I melt up a pound of Crisco along with the wax from a toilet ring - the toilet rings aren't pure beeswax anymore but the mixture of that and the crisco seems to work well for me - it all depends on the temperature you're shooting in - but Crisco will work fine to start out
Capper - this isn't necessar to start with as you can put the caps on the nipples by hand (just as many did originally) - but if you find a capper that will allow you to fit a cap on the nipple of your revolver, it speeds things up
Like anything else in this life, "you get what you pay for" - that doesn't mean you have to purchase the most expensive item - just be prudent and look for the best quality at the price you want to pay.
I'm sure others will chime in here with help. Welcome aboard and good luck in your new adventure - all I can say is that you're gonna love it! Lot's of good fellows on here with lots of experience so don't be afraid to ask! The only dumb question is the one you don't ask! Have fun!
