You may want to make sure it's your thing before you start buying a whole bunch of stuff. Just a suggestion.
For most people the Billet Box seems to be an all or nothing endeavor. Either they wind up loving it and no amount of trinketry is enough, or they just don't take to it and it goes up for sale.
The most important component is the RBA's/bridges. My advice, whatever that may be worth, would be to get a couple proven RBA's and see if the whole Billet Box... thing is for you.
Like I say just a suggestion. I've seen a number of folks go hog wild at first and then a month or 2 later it's all up for sale. OR, several months later they now have 5 Billet Boxes, 7 RBAs, 12 sets of doors, 11 buttons and 23 drip tips.