I'm not 100% positive, but it sure looks like a CVA Mountain Rifle.
The earliest models had Douglas barrels that were made in the U.S., but the later models all had barrels that were made in Spain. They're known to be very decent shooters.
The used gunshop value is about $150 or so, depending on the condition of the barrel.
You'll need some of these things to start shooting:
1. Powder measure to measure the powder charge.
2. Flask to dispense powder into the measure, so not to dispense from the powder can.
3. Capper to help apply caps without using your fingers.
4. Nipple wrench to be able to remove the nipple for cleaning it.
5. Short starter to help get the patched round ball started down the muzzle.
6. Rod accessories:
a. cleaning jag to help grip a cleaning patch for wiping & cleaning.
b. patch worm or patch puller to grab and pull stuck patches out of the bottom of the barrel.
c. fouling scraper sometimes comes in handy to clean the barrel breech.
d. cleaning brush for your caliber for removing stubborn deposits.
7. Nipple pick to clear the nipple of debris.
8. Bore Butter or Wonderlube to lubricate patches for loading, and the barrel after cleaning and to help prevent rust.
9. Patches, .015 thickness, pre-lubed or saturate them with Bore Butter yourself.
10. Balls, .530 diameter
11. Powder
12. #11 Percussion caps
13. BP cleaning solvent - will help to clean the gun without using water, and is very helpful if using Pyrodex.
14. BP Cleaning rod or kit, it's longer and has a handle for easier cleaning without using the short ramrod.
15. Ramrod - I recommend buying a wooden dowel nearly as thick as the bore caliber at a hardware store for about $1. Drill a hole in a wood or plastic ball, a hunk of plastic or wood to make a handle for it and this will help to make ramming the bullet or ball down the barrel much easier by giving better leverage. Mine are 7/16 th's in diameter and have never broken.
For a .54 caliber percussion gun, usually the common starting point for working up an accurate load is to use the .530 balls and a lubricated patch with a thickness of .015.
There are other diameter balls like .535, and other patch thicknesses, like .005 (too thin), .010, .018 (blue stripe pillow ticking), .020 (maybe too thick).
The recommended starting powder load is the same number as the caliber of the bore, about 50 - 55 grains by volume.
If buying .535 balls, start with a .010 patch or loading may be difficult.
Did you ever imagine that this could get so expensive?