If it was me and based upon what you've said and that you've already ordered it I would keep the PM
I'd probably get one of the voice modules next along with an envelope generator (pams will work well for this) and something like an SQ-1 (yeah yeah I know external, but small and quite cheap) - treat this as a stopgap until you decide what you really want to use for sequencing
After that I'd want one of the fx modules and a quad cascading vca (for modulation purposes mainly) and some basic utilties (at the very least a kinks - for the price and size it is really worth it)
I would then play this for quite a while and try to grow organically - ie I need a XXX module
Regarding the Bitbox - only you can decide, but a possible solution is to get more stop gap modules - I find I want as a minimum for percussion about 4-5 'voices' - kick, snare, open and closed hats and one other thing for accents or whatever - I find using plaits for primarily hi hats, as I was for a while a bit of a waste, personally - but it does sound great!
The polyend module I would leave for a long while in the future - I'd work out how to use the other modules first and only add this if/when you feel it's necessary
"some of the best base-level info to remember can be found in Jim's sigfile" @Lugia
Utility modules are the dull polish that makes the shiny modules actually shine!!!
sound sources < sound modifiers < modulation sources < utilities