If you think that you can shoot a firearm and then not clean it for a few months, I suggest you don’t purchase a muzzle loader. Every propellant used in muzzle loading is corrosive at some level. The traditional black powder is very corrosive. When you are hunting and a follow up shot is required, there is no need to clean the bore. Get the reload over and continue the hunt. The time to clean is at the end of the day. When you are practicing, it is recommended that you at least swab the bore every few shots to ensure accuracy.
Disassemble the rifle as recommended by the manufacturer. The cleaning process will vary depending on the type of weapon: flintlock, percussion cap or inline. It is very important that you remove the residue from the black powder off the metal and wooden parts. Black powder residue attracts moisture and moisture causes rust. Once all the residue is cleaned off, a coat of oil will protect the metal. Be sure to clean everywhere, a forgotten spot today will rust tomorrow.
To use a brass bore brush to clean the barrel is a personal choice. By using a bore brush and soapy water, the protective coating of pantina is removed from the bore. Some hunters insist that the pantina provides better protection for the metal. Like most thing related to firearms and hunting, it is a personal choice that deserves your own research. That is also true of all the different cleaning systems and cleaning solutions sold for black powder weapons. It is best to experiment and make your own decisions. Just remember that nothing is wrong with hot soapy water and elbow grease. No matter what you do, it takes time to properly clean any firearm, modern or antique.