Keeping in mind that this is all new to me, I will ask the following: What about a powder measure? How often do you need to clean it during an afternoon of shooting? What solvent for cleaning? What is the most common mistake that can lead to a dangerous situation while loading and shooting?
In the N-SSA, we use little plastic tubes to store our powder and bullet as a "cartridge"
You set these up in a tray, like a shotshell holder, and charge the tubes with powder, and then stick a bullet in the end like a stopper.
Alternatively, you can make authentic cartridges like I did here:
Many places sell brass or plastic powder measures. Just google "powder measure". These measure out powder by volume. You'll need to be consistent in how you fill them and top them off to get consistent results.
I bought a small electronic scale from Midway USA made by Frankford Arsenal for like $25. It measures to the 10th of a grain. I use the powder measure to dump into the scale, and then add or remove powder until I get exactly the right amount by weight. But I am shooting for competition.
Depending on what you are shooting, you may shoot all afternoon without cleaning at all. The RCBS Hodgdon Minnie Ball bullet, for example, has an extra-large grease groove and you can shoot a lot without stopping to clean. Even with standard Minnie balls I can shoot a dozen or more before it starts to get hard to load.
Again, I shoot in competition, so I usually run some patches down my bore after every course of fire. In practice, that is after every 10 shots. At a skirmish, it could be 12 or 15 shots in a 5-minute event.
Here are some mistakes to watch out for:
1) Make sure you have not under-charged (no-charged) or over-charged your cartridges. Sometimes you can't see the powder as you dump it in the barrel. If you have no powder in there you may not notice. Then you ram the ball in on no powder and now you are done shooting for the day or until you can pull that ball. I just did that a couple of weekends ago and bought a CO2 discharger to blow it out of the gun.
Over charges are probably not as big a deal with BP guns as they are with smokeless powder guns. I shoot target loads of only 40 grains or so, so even if I double-charge it's only 80 grains which is not a whole lot more than the service load of 60 grains. Also with my plastic cartridge tubes if you double-charge it's hard to stick the bullet in the end as it is too full of powder.
So when you have all your tubes set up in the tray and they are charged, get a flashlight and look down in them all - any that are empty or over-full will stand out.
2) Make sure you seat the ball all the way down on the powder. An air gap is also known as a "barrel obstruction" which can result in a kaboom.
3) Wear safety glasses.
4) Realize that BP guns are real guns and will kill just as easily as a modern gun.
5) Get a "breach scraper" for your cleaning rod. This is an attachment with a flat blade that scrapes the face of the breach. If you don't do this, carbon deposits will build on the face of the breach and may start to glow like an ember during shooting, especially high volume shooting. This can cause a cook-off when you are dumping the powder in.
6) While loading, never put any part of your body over the muzzle! (see cook-off above). Set the ball in place with your thumb and forefinger. Do not "thumb the ball" into the bore.
For cleaning, it's hard to beat Ballistol. Soapy water works, too. I usually start with soapy water and then switch to Ballistol.