That is one gun that anything other than a very light cleaning of the rusty parts would do it a great disservice. If it were me, I would use some 000 steel wool with a little oil on it to lightly clean only the red rust off the metal parts and go no further, treat it like you are carding a barrel that you are browning. You need to know how to carefully disassemble the gun without damaging anything to give it a proper cleaning and don't clean the stock other than applying a tiny bit of Renaissance wax.
The inside of the barrel is probably dark and rusty, the gun may be loaded, 30% of the old guns that turn up are. Your ramrod will tell you if it is. If it stops before it gets to the drum the nipple sits on it may be loaded.
If you want a nice-looking attic condition wall hanger it wouldn't take much work, if you want a shooter you will have to have some serious gun building skills and knowledge. It appears to have been converted from a flintlock to percussion.