Might be someone here that is geographically close to you. But, we seem to be back to very few members having their general location on their profile, so we don't know where you are. Thus can't refer you directly to help.
Almost anyone here will advise you to use real black powder regardless of flint or cap lock type. But with the flint it is a must. Not sure where to send you to get it. You can order it, but have to order a bunch to break even on the haz-mat fees.
Adjustable powder measures are easy to come buy, even Cabelas has them. Remember we are measuring in grains by
Volume Not by Weight. A general starting load for load development seems to be a match between number of grains and bore size, so for a .50 caliber start out at 50 grains and work up from there. As was said earlier, there are numerous threads on here dealing with load development.
Something to pour the powder from into the measure is a good idea, either one of the spouts designed to fit to a specific brand of powder's can/bottle, or some type of flask (spilled powder can be hazardous) such as this...
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Avoid prelubed patch material, but, don't be afraid to use precut patches for now. Again, there are a ridiculous number of topics here relating to patch lube.