Your first build shouldn't be this small. Small builds add a huge layer of complexity. There isn't any room to expand or fix a problem or modify the build once you've used it for a while.
Small builds that are "good" are much, much easier when you're experienced.
Buy a reasonably sized case like a Mantis, Behringer GO, etc. Try to get your first iteration built using about half of your space. Then as you grow, you can revise your case, push your system in the direction(s) you want to go, and not get stuck with a system that you can't fully utilize.
Of course, you can always buy a second case/rack. But it's a lot cheaper in the long run to just build in a case larger than you need.