Most people will advise starting with .530" balls. If it were me, I would start with .526". Life can be such a freakin' battle sometimes that the last thing I want to do is fight with my rifle while loading it. I like to keep some alternative ball sizes handy, though... .520", .526", .530", .535"... All of those are available precast and/or swaged, and in my opinion it is worth investing in an assortment of ball sizes to have on hand. Your rifle will tell you which it prefers.
Years ago, the experts were advising 2F powder for anything .50 caliber and above, and my dad preferred 1F in his 12 gauge Scott double. I still use 2F in my .54's. However, a lot of people now seem to be shooting 3F in everything. It is more energetic than 2F, so you might get away with a slightly lighter charge. As with the balls, it can be worthwhile to have some alternatives available, so when it's convenient you might get a bottle of 2F to try. Different brands of powder (e.g. Goex, Swiss, Scheutzen, Olde Eynsford, Grafs...) in the same nominal granulation may burn differently, also. Again, your rifle will tell you what it likes if you experiment.
However, if you already have .530" balls and 3F powder, I think you are probably good to go, at least for a start.
Be safe, and have fun with your new rifle! A custom .54... We'll be wanting some pictures, you know.
Notchy Bob