> The problem are the gates.

I assumed he was going to get four envelope generators, four oscillators, and four VCAs. Which personally I wouldn't do as for that money and space I could have a great monophonic setup with enough different filters to sound like a whole room full of different synthesisers, instead of an OK polyphonic setup. But if you really need modular polyphony for some reason, that's probably the way to go about it.