to me the things that you need primarily to use with the synths you do have are modulation, utilities and some sound processing
2 voices in a case this size is too many in my opinion unless you are into tiny modules etc because you will not have the room to adequately support 2 voices properly and the above in a single 3u/84hp case - and small modules are often not great to play with - especially if bunched together
do you really need an ADSR or do you need an envelope generator? - most people don't actually use ADSRs that much - AD is much more common - ADSR really only if you play it with a keyboard
I'd rather buy doepfer than the b-company any day - relatively cheap and generally simple building blocks, but solid builds and knowledgable staff - Dieter may even answer himself
"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