Victor: Did your rifle come with an instruction manual? If so, read it thoroughly before shooting your firearm. If not, you should be able to find all sorts of information about the Enfield rifle, by Googling it. Its a good place to gain some information. In the meantime, this may help: .58 caliber Enfield rifles like yours would normally be loaded with a .577" Minie bullet. The Minie was designed with a hollow base....the "skirt" of which would flare out when the powder charge ignited and gas pressure forced the bullet into the rifling. Though it may take a bit of experimentation on your part to find the right powder charge for good accurate shooting in your rifle, somewhere between 50 and 60 grains of Goex Ffg powder will likely do, to start. Note: It doesn't take much powder to expand the Minie bullet, nor was a lot of powder used in original rifles. It is also possible to use solid base, .58 caliber bullets in your rifle. As mentioned, Lyman makes good ones. Likewise Lee. You can also check out the Pedersoli website. Pedersoli manufactures an 1861 musketoon similar to yours. This company also has the proper sized bullet molds for this rifle. Worth a look.
Your musketoon should take a "musket", or "top hat" cap. These caps are fairly large and look somewhat like a "top hat". Most sporting good stores in your area that sell black powder supplies should have them either in stock, or can order for you. One of the site sponsors: Al Flaherty's Outdoor Store is close to you. It is likely that shop will have everything you need. Though not a site sponsor: Shooter's Choice, in Waterloo, is a Pedersoli dealer. They will have all the accessories, like spare nipples, bullet molds, etc. A word of caution: There is nothing that will ruin a nipple faster than dry firing the firearm. Don't do it! The hammer strikes on the nipple mouth will soon dub it over and render it useless. Always ease the hammer down gently onto the nipple when not in use. Or, use a nipple protector. This can be as simple as a piece of thick cloth, rubber or plastic between the nipple and the hammer face. Or, you can purchase a nipple protector. Its also a good idea to have a spare nipple on hand, just in case. If treated with care, a nipple will last a very long time.
One thing you'll soon discover is that black powder can be a bit messy to deal with. Cleaning the firearm thoroughly after use is a must. But not that hard to do, once you get the hang of it. Be sure to read up on how to properly clean and maintain your firearm first, before firing it. There are also plenty of highly experienced black powder shooters on this forum that can also help. One quick tip I'll give you right now: Pick up a bottle of ordinary isopropyl alcohol, at your local pharmacy. This is one of the best black powder solvents I've used. Very effective and cheap. One pass with a wet patch downbore, followed by another clean patch or two and your rifle's bore will almost perfectly clean the bore between shots. By the way, if you have an old flannel shirt, etc., these can be cut up and made into good cleaning patches. You'll still have to give the firearm a good cleaning at the end of the shooting session, but this will get rid of a lot of the mess. Anyway, hope some of this is useful.