I like giving myself obstructions and believed I could achieve what I want in 3u/104hp as I'm using a set up that involves additional components, eventually I'd like to only use my laptop to record into the DAW. But you're probably right on one or both accounts, replace Maths, fill that space with a proper envelope generator and get a bigger rack.
-- Excommunicate
I definitely understand the concept behind "deliberate limitation", but I think you'll find that the obstructions that will result in this circumstance are NOT helpful. For example, you mention wanting to record directly...and this IS possible with some of Expert Sleepers' modules, but the space limitation eliminates them from potential choices here.
Also, when I was talking about "replacing" Maths, I was referring to replacing it as a source for envelopes. Maths is STILL one of the cornerstone modulation sources in Eurorack, even with its 20 hp size. But what makes it amazing for modulation involves using it for quite a bit more than JUST envelope generation. Plus, you can tandem Maths with a lot of things, including other EGs; one neat combo that comes to mind is using it with an Intellijel Quadrax + the Qx expander. Loads of abuse potential there...