I'd say its too small because of heat and trying to wire the components. I'm presuming that you're going to put an E-Stop (or "OH SHITTTTT......!!!") Button in somewhere in your system for safety? If so you'll need a relay....how about fuses to protect the VFD, drives, PSU? There doesn't seem enough room for all of that?

There's always more components than you initially think which take up more room than you've allowed for...called sods law :)