1 what is your use case for an output module? most people do not need these - if you need balanced output or a headphone output - then get something that specifically does that - otherwise simple attenuators and adapter cables work perfectly in most cases - and are always a better starting point than an output module - worst case is you end up with an output module and some attneuators - which is no bad thing - attenuators are always useful
2 if you are intending to expand the number of voices - it may be an idea to look at either bloom or marbles instead of a turing machine - both have more channels and have built in quantizers - marbles also has a lot of gate features and a random source -all useful in a small system and this would mean you can put off a separate quantizer, potentially indefinitely - if you intend to use the mimetic digetalis to record tracks and replay them then the
3 I would go with veils or intellijel over the doepfer vca - because they are slightly less cramped and offer more features
4 I would start with a more fully featured modulation source - by that I really mean less cramped and more easily controllable - personally I recommend Maths as a good first modulation source - not only because it is a classic and is reasonably well laid out, but also because the unofficial illustrated manual elevates it to being one of the best documented modules and it is an excellent resource for learning about how modular synthesizers function and techniques such as patch programming - invaluable
5 I feel this system is quite unbalanced - way too much sequencing and not enough of everything else - I would start with 1 sequencing/modulation option - pnw or marbles - the bia - veils and then add maths and some sort of effect - either an anaolg filter or something like an fx aid xl and then the utilities that are needed to make the most of these modules - I always suggest links, kinks, shades as a good starter utility package - and then another voice - and then whichever of pnw or marbles I hadn't bought eearlier
6 if you have a more expanded 'dream' rack that this is a stepping stone towards - then I would share that as well - it may be that a better path is possible to it
7 don't buy modules just because they are cheap - or affordable - buy them because they are the modules that you need - if the quantizer that fits all your requirements is 2 times the price of the cheap quantizer that fits 80% of you requirements - then save for the more expensive one (or dig deeper in your pocket) - because you probably will end up with it down the line after getting frustrated because feature x is missing
"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