well that was a lot to read!!!

so you want a modular synth that you can sequence externally that has 2 voices (nominally bass and lead) and when combined with your pedal board will be able to produce music in the style of My Bloody Valentine/Alessandro Cortini

and here is another!!!

1 - get a bigger case - I would go for a tiptop mantis - it is very portable (similar to a guitar - carry it on your back) and has very good power - does not include parts that are irrelevant to some extent - especially as in your use case you are only using the buffered mults - and for all the 1u that you have added there are often cheaper/better solutions in 3u - get some blank panels to cover up the gaps (or make some) - you only need one buffered mult for example - you could use a mutable links for this and have 2 utility mixers as well in 4hp - I would at least have a play with this idea - don't fill the case - concentrate on what you think you want to fulfill your current goals - at least this way you will have space to add the modules that you find you need in the future without having to buy another case almost immediately

2 - if you are married to the case then you really have too many 'feature modules' and not enough support modules and not enough of the right support modules and a lot of redundancy and a mixing strategy that has not even been been considered

take out:

the lofi junky and get the pedal - it's cheaper, takes up no rack space and you loose very little in terms of modulation - which you have very little of anyway

sloths is a good 2nd modulation source for adding to another but not great as a primary modulation source imo - remove this and replace with say pamelas new workout - possibly get a 1u sloth, if you want to add some chaos and can find some way top boot something out of the top row - quadratt

optomix - I would remove this as well - it's big - plaits already has lpgs internally and ripples has one too plus your mixing solution needs improvement anyway

tiptop z4000 - replace this with either something smaller - do you really need adsr (probably not) - with pams above this is probably completely redundant in any case

that frees 34 hp and uses 8 (pams) which leaves 26hp

I would want vcas and mixing for everything else and a lot more in the way of utility than you can fit in this size case - plus aiming for a MBV esque sound I would want more modulatable reverb and delay modules - a couple of fx aid xls for example

Even removing all those modules - I see a lot of mono audio outputs (plaits (2), sto (3), ripples (3), pedal board return(1) = 9 audio outputs) and no way of mixing them to stereo - which is what your headphone module is expecting

currently the only mixer you have is duatt - which mixes 2 channels to one - yay plaits is covered - maybe

I would want a quad cascading vca such as veils or intellijel - but there won't be enough space for these

I think the best bet would be to go for a selection of Happy Nerding mixer modules - some combination of 3x VCA, PanMixJr, 3x stereo mixer, 6xMix will get as close to solving the problem in the available space as possible - probably won't be able to mix all outputs all of the time

3 - replan totally - ignore anything to do with cases for now work out what you actually need

2 sound sources - plaits is great as 1 of these/sto is fine for the other
pedal i/o - I would consider the ADDAC as it has 2 channels!
1 or 2 good modulation sources
a filter for the sto
a quad cascading vca - mutable veils and intellijel are really the only 2 I would consider here
whatever in rack effects modules you want - as I said above - a pair of fx aid xls would be a good choice for this style of music

Once you have all of those in a big (make it as big as you can, it is a sandbox, not an actual rack) modulargrid rack work out how you can provide modulation for all the modules - do you have enough - almost definitely not - spend some time thinking about how utility modules such as attenuators, mixers (especially matrix mixers), multiples, vcas, rectifiers, logic etc can leverage a relatively small number of modulation sources and what other utility modules you may need - kinks is an exceptional utility module in this regard - it can turn 1 modulation source into 7 related but different modulation sources, for example

Now consider how you want to mix the audio - do you want submixes before/after/between effects etc - does the mixing want to be voltage controlled? do you need stereo output? if so consider how you are going to convert mono to stereo and how you are going to mix stereo signals - if it was me I would want to be able to run effects in both parallel and series, over all the sound sources, individual parts and all points between

add all the utilities and mixing into the rack - don't rule out Doepfer and Ladik and other more inexpensive brands - if the module does what you want then use that over a more expensive brand

now take some copies of that rack and try to consolidate it into rack configurations

try some with 1u rows - the 7u/104hp intellijel case may be a good starting point for that one, or a mantis or even the palette - maybe you need to go for a micro version of a few modules - maybe you need to take one fx aid xl and one regular one - to enable you to cram what you need into a case - preferably with some space available - so that you can add something you find interesting down the line, without having to throw something else out you need

and then get a minimum playable version of what you need and start playing with it - add the other modules slowly - maybe spread the cost out over a year, or longer - so that it is affordable

"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