Hi Humanoid01,
I like your case choice, bit pity you planned it already very full. I would like to advice you strongly to keep some blank space for future extension in your rack free, having that said... consider to ditch the Marbles and Alter modules either one of them or both. Once you gain more experience you still can consider them to add later.
Marbles = 18 HP = 7.1% of your total rack capacity
Alter = 16 HP = 6.3%
So these two modules together = 34 HP = 13.5% of your total rack capacity, that's about one-seventh... are you sure that's worth it?
I see that Baltergeist and Troux already answered two of your questions. What I did is I made a rack configuration, shown here below how it could look like with your own comments and that O'Tool Oscilloscope, that one saves some space.
You still could consider to exchange the 2nd Doepfer A-140 ADSR with another brand's ADSR. There didn't come one to mind to me for your case here but perhaps you could consider an EG from Erica Synths?
That matrix mixer I ditched it and replaced it by the Doepfer A-138p & A-138o combination, this is chainable with just a 2nd 138p and then you get 8 channels; but that's for the future ;-)
I ditch one of your Kinks modules, you had two of them in your rack. Start with one, if you really love that one then get a second unit.
That Bastle Instruments - Cinnamon filter, I don't know it, might be indeed a nice module but it's a nasty one with 5 HP so next to your two chosen Erica Synths - Pico modules, I planned another 3 HP (2+1) blank space for yet another Pico (or other 3 HP) module, so it's nicely filled in again in the future; up to you of course. Instead of the Cinnamon you could consider the Doepfer - A-124 (Wasp filter) or the A-106-5 (SEM filter). I can recommend both, the Wasp filter can provide perhaps a bit more of a sonic adventure, the SEM is a bit more subtle, both are nice filters.
I have a bit lack of time so my rack layout suggestion here might not be ideal but is perhaps an idea of how to get started, the rest is now up to you to plan it the way you like! :-)
Good luck with it, have fun with modular and kind regards, Garfield.
For review reports of Eurorack modules, please refer to https://garfieldmodular.net/ for PDF formatted downloads