Let's see if I can finish this without accidentally closing the wrong tab this time...
Anyway, it can be a help to have everything by the same company...except for that moment when you see something done by another firm that's improved on the functionality that's only dealt with in basic terms by your 'primary' firm. That's why the 'mix-n-match' method works and is so prevalent. But there's nothing wrong with keeping most of your modules under one firm's label. In fact, if you opt for companies that have long track records, extensive lines of products, and a big user base, that tends to be a good indicator of a firm that's suitable for being a 'primary'
But at the same time, there's also excellent companies that have small lines because they work along certain specialties. Take Shakmat Modular, for example; most of their very short line deals with clock-based issues, and that's a great indicator of a company that knows their stuff about that particular peculiarity of modular synthesis. Another example: Audio Damage, who concentrates mainly in audio processing modules...same idea. When you see a concentration like that, again, you tend to be dealing with a company that knows their stuff and which opts to specialize instead of going full-spectrum on their product line. Also, look for 'discontinued' modules that have been replaced with majorly-improved version; when you see a lot of that, again, that's a company that keeps pushing what they can accomplish with their products and also, a company that's both likely to be listening to its user base and striving to push the hardware envelope as components and technology improve. Mutable Instruments, with their discontinuation of the much-used Braids to give us the majorly upgraded and downsized/downpriced Plaits, is a great example of this in action.
As for Erica, they're truly the Latvian Voodoo Masters of the Black Art (hence the module color scheme? hmmmm...) of International Air Shipping. Their stuff is bang-up, especially their Pico 3 hp modules, the frequent tube models, and their powered cabs. MakeNoise's Tony Rolando's probably got Don Buchla tied up in his basement, too...the obituary was just a cover story, natch...because he's pushing many of those classic West Coast ideas off into wild zones. Either are kickass places to start with a prebuild, because you'll be getting something from firms with great support, and people running the show who know their stuff. But if I were going to go with a patchable...oh, wait, I probably AM...to match with a small modular expander cab, I'm gonna have to go with an Arturia rig. After all, they've got Yves Usson giving them a leg-up, and the form factor they cooked up with the Minibrute 2 + Rackbrute, with its portability...it's hard to argue against that! Plus, aside of the (cough, cough) Origin, Arturia gets things right and they're available at your local Circle-K (well...almost) like Roland, et al. The stuff I have from them gets used here, and it doesn't screw up. I like that.