Congrats! That lady is a keeper for sure!
Leather or lead isn't really going to make a heck of a lot of difference. I personally use lead, because I have difficulty keeping larger flints from moving in the jaws of the frizzen on occasion with leather. I just hammered a ball flat and trimmed it a bit to fit.
I would get on over to http://www.trackofthewolf.com/ and take a look at what they have to suit your needs. They carry a lot of the stuff specific to flintlocks that can be difficult to find other places.
You'll need a cleaning jag and patches large enough to fit the bore. I use windex to clean my black powder guns, then oil with CLP.
If the gun does not have a touch hole liner, that might be worth looking into, a "White Lightning" liner will improve ignition speed.
If it was my gun, I would also make or procure a range/cleaning rod to use with the rifle, so as to spare the supplied wooden ramrod. A piece of brass or aluminum round stock threaded for a cleaning jag on one end and a t-handle on the other works well.
With the smooth bore, patching isn't as much of a concern for you as it would be if you had a rifle. Most smoothbores of the period used paper cartridges, with the paper acting as patch. You will need wadding if you plan on shooting shot/buck loads out of it, which is what they were intended for. TOTW sells wads in the appropriate size, I'm sure. They sell shot too, #4 buck is sold in a 5lb bag for $25, which should make for great fun and turn heads at the range!
It goes without saying that you'll need real black powder to enjoy your flintlock. I would stick to FFg.