I should say I'm trying to build a portable techno system myself right now, getting a lot of great advice from others here.
One particularly transformative bit of advice: the Metropolix is a beast of a pitch sequencer. If you're trying for two voices (maybe a lead and a bass line), the Metropolix is a solid answer. I'm buying one myself.
Another transformative bit of advice: an external drum machine works really really well. You have a lot of space with this case, but my guess is you'll find space runs short incredibly quickly. An external drum machine saves a tremendous amount of space, and a tremendous amount of money as well. Plus, you know, they're fun.
Are you sure you want to have a dual purpose of melodic techno as well as ambient with this build? It seems like one of the consistent pieces of advice I run across is to focus your build on one area; build it to do one thing really really well before trying to cover more bases. Noodling around with modular is plenty of fun, but if you want your build to actually make good music in some specific genre, build for that genre in mind.