:imo: The Bess isn't a bad choice if you keep in mind that it's a large bore fowler and treat it as such. The only "bad" thing is that like most military muskets, the cock is large and travels through a longer arc. Time between trigger pull and ignition will be a tiny bit longer so if you're pass shooting at waterfowl or trying you hand at dove, etc., you'll have to remember to follow-through.
As for shooting ball, your best bet will be to measure the bore and get or cast balls at least .020" smaller than bore diameter. Actually, in the real guns the British used a ball about .690" so they could continue to shoot as the fowling built up. Patching the ball will be a plus for modern shooters and you might start about .015" with patching and make sure it's well lubed but not dripping wet. Have found about 80 grains of FFg to work pretty good but your gun may like something else...not a bad reason to tell the boss, "Well, dear, i have to shoot again today to find the right powder charge" :thumbsup:
As for the rest, some will depend on whether you're just shooting a big bore fowler or going to try the re-enacting game. If you're just starting out you'll need a powder measure, probably a combo pick/brush to clean the pan, some sort of holder for the powder (whether flask, horn, or pre-rolled paper cartridges is up to you). If you are going to do this fairly often, a spring vise for the lock is helpful, as are some sort of turn-screws (screwdrivers) depending on your use. I'm sure others will have more to say but these are a few of the basics. Obviously, you'll need patching, wads & ards to shoot both shot and ball. Outfits like Track can provide these in the right size. At some point you may decide to make your own but for starts it may be much easier to use "store-bought" till you find the size you Bess likes best.
As for cleaning, if you shoot-you clean. There's no putting it off with muzzleloaders. You may hear many ideas about what to use but I'll just say this. There is nothing in black powder residue that isn't water soluble and can't be removed with plain water...I've done it for years. A little detergent may make things a bit easier but I've never found much difference. Just be sure the bore's clean before going to the oil/grease for storage. Some folks are now praising Ballistol and that may be one of the better products currently available. It's a cleaning product developed by the German Army during WWI and has been used continually since. Seems to work well mixed 50/50 for patch lube and straight for cleaning/storage. As for lube, I've used Crisco, tallow and even salt-free lard. Olive oil is popular too, mixed with beeswax...seems that if it's slippery somebody uses it. My only take on it is KISS...keep-it-simple-stupid!! That's me...Senor Stupid. Just shoot and have fun but remember to clean up after. Big bore guns are relative forgiving about patching, wads, etc. just don't try to break the speed-of-light!! Good luck and don't be bashful about asking questions. Some of us greybeards still have all 10 fingers, we must know something, though don't bet money! :crackup: