I don't think there is much in the way off keeping the break dust off unless you use different pads and what not. However you can use any sort of sealant or wax, although I think a nuba is not worth it due to limited longevity and it seems to attract more brake dust. I have black powdercoated rims also, with a mag lip and use Klasse SG and Ultima Paint Guard Plus. Normally for me its a wash weekly with a spray wax which is what Ultima PGP is and then klasse every couple months when I pull them off and do a polish on the lip and everything.
I get my small amount of brake dust on occasion but nothing to bad and I clean them so often that I have never had a problem with caking or what not.
Last note, I wouldn't really use a degreaser or apc since they have been repainted and just me being me, im skiddish of using degreasers on paint. There are exceptions though where a light degreaser can be used as long as it is removed quickly and in a heavily diluted ratio i.e 10:1. I suggest just using a regular car wash shampoo such as Megs Gold Class or ONR (my favorite) for cleaning.
hopefully this helps a bit or at least points you in the right direction.
