I have three percussion-ignition black powder guns that I built from kits when I was in middle school and high school.
My first was a .45 caliber derringer style. It looks a lot like yours, but a bit plainer. The next one I did was a 1851 Navy Colt Revolver. That one got a little more in-depth because you had to work on the revolver mechanicals to get it "timed" correctly. My final one was a Kentucky pistol in .45 caliber. That one had a LOT more wood working to do on it. The Kentucky pistol is also incredibly accurate. I can easily put 5 shots into a baseball sized area from 15 - 20 yards out. After about 5 shots, though, the pattern starts expanding because of the dirty barrel.
All three guns are fun to shoot. But "american lockpicker" above is right -- you really need to clean them. Black powder burns REALLY dirty. After a few shots with the single shots, or a couple loads in the revolver, the barrel is so dirty that I think it affects the accuracy of the gun. You may want to check the gun's directions and see if you can shoot Pyrodex instead. That's a lot cleaner-burning.
By the way -- it looks like you really did a nice job! The lock plate inset work looks really nicely done!
Have fun with that little guy!
ps -- I once loaded my derringer with some shot to see what kind of "pattern" I would get. Holy cow!!! About 6' wide pattern at about 15' away! Talk about a "scattergun"!!!
Oh -- One other thing ---- You really don't need Hoppes or CLP to clean up with black powder. It just takes dish soap and warm water. They are messy -- but they clean up pretty easily. Just be sure to oil it well after you wash it.