OK...let's go through this...
1) How do you mean "use" here? Technically, you can have as many controllers as your build has patchpoints, if you wanted to go that far. If you're trying to use them as simultaneous CV sources for the SAME function, though, you'd need an adder to arithmetically combine the CV values. However, this is apt to get a little bit OUT of control, as you'll have to juggle the behavior of both the BSP and uFreak at the same time and keep your mind on what the CV combination results are going to be...which is apt to get VERY tedious. My suggestion would be to pick ONE controller and stick with that...especially given that this build only has a single VCO in the first place.
2) This isn't "high priced". Trust me, the cost could go LOADS higher, even in 3U x 84; load it with Cwejman and Schippmann modules, and you'll see what I mean. But I can tell you right now, this build is neither suited for real generative work nor could you call it "suped up". Fact is, it's kinda underpowered...with the cab itself being the main problem here. So if I were switching out anything here, I'd start with the cab itself. These little skiff builds might pop up on YouTube and all that, but much of that YT activity is pretty misleading, as smaller systems like this are actually rather difficult to configure...sometimes even for experienced modular users!
3) See #2 above. Seriously, I wouldn't be worrying about modules right now...the case itself, and the lack of space it's causing, is the biggest stumbling block here. And while the Cre8 cab is $199, another $136 could've gotten you into a 2 x 104 powered cab, the Tiptop Mantis. Fix that first, THEN start exploring module options.