I assume you’ve got a set of nuts and a few hex equivalents for wider cracks. Have a think about the placements you’ve made with those and let that be a guide to sizes. For Camalots I’d say go for 0.5, 0.75, 1 & 2. You’ll want about 3 smaller cams as well but I don’t know how well the small BD units rate against Aliens or Metolius TCUs which were always the way to go. If you must double up right from the start go for 0.5 & 0.75.
If you get a chance to climb with a mate’s BD gear before you buy then you’ll be certain that you’re getting what you want. There’s a lot of personal preference in anyone’s rack so hope you can get a range of opinions.