it's an interesting concept...
regarding starting very small, I wouldn't personally, at least regarding case
by the time you have an es9 in the rack you have taken quite a lot of space already and when you add some decent modulation sources, some performance controllers and the utilities that you need/want to support all this - you will be around the same as a regular starter case - 84-104hp/6u - possibly with a little room for expansion
small cases are relatively expensive - especially ones with 1u rows - so unless you are smitten by their cuteness, as so many are I would forgo these - also you pay a lot for power and any utilities/functions that are often encouraging you to buy specific modules to get them to work - which there is nothing wrong with but particularly in this case you are not looking to use midi or audio i/o from the case
aim to buy something like a mantis or doepfer lc9
but start with the modules you actually want and need - paying attention to these points and then putting the case around them seems like a much better solution to me - remember you don't have too fill a case in one go!
"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