Great gun I like twist P's. I think I would leave it alone from what I can see there is good color on the barrels. Edgar is right. If you want to shoot black powder use brass hulls and make your own unless you r not good at... if you have changed your oil over the years and your motor has not locked up you can probably do it. I think everybody should shoot a little black neet stuff.

Some people like Fords and some people like Chevys. Some people even like Yugos
If you like extra work shoot Black Powder. If you like to shoot use RST rounds or the equivalent. (after you have the gun checked over by a competent side by side gunsmith)
Currently all my older Parkers are used with smokeless loads appropriate to the age of the wood. Recently I have been shooting Damascus or twist shotguns almost exclusively with loads appropriate for the age of the wood.

In my opinion there is no reason not to shoot low pressure loads like RSTs in a good quality Damascus or twist gun. The key is to look for deep pitting or rust on both the inside and outside of the tubes. If the barrels are free of that and wall thickness is up to specks I don't foresee a problem. Keep in mind this is an educated opinion, and it's still an individual decision.

May I suggest that a starting point for understanding what you bought is to read what the manufacturer said about it when the gun was made:

Something I forgot to mention, it's a good idea to "ring" the barrels. Remove the barrels from the receiver and carefully hang them with a strong cord. I usually tie one end of the cord around the extractors and suspend the tubes by holding the free end of the cord. Take a brass hammer and LIGHTLY tap each tube, they should ring like good wind chimes. If on the other hand the sound is dull it might indicate corrosion under the ribs and should be checked by a professional. A customer once brought me a nice Ithaca double that he was unable to clean a spot out of one of the tubes, on checking I found that the barrel had rusted through from under the rib and there was a hole about 6" in front of the chamber and this was on a steel barrel. The gun otherwise looked fine but responded to the hammer tap like a piece of lead.