12G SDI is super flaky, I wouldn't invest into that technology, It just doesn't work well.
30 projectors per side
Each PC can handle about 11 outputs from 3 different GPU's. But since you're wanting each projector to have it's own source, that's 11 4K textures each PC would have to handle. That's going to be over 91 million pixels. At that point you're going to be over the render count per GPU. So even with a fully loaded PC, you would need 3 PC's per side (6 in total) to do this, but since you're over your pixel count per rendering GPU this is a moot point.
Realistically you would want 3 4K outputs per PC with 1 GPU to keep your PC happy. But this means you would need 10 PC's per side (20 in total), so now comes the kicker.... Sync.
You could get away with this if you're using LTC to drive all of the content, but that means a LOT of work with your content to get it all working the way you want. You could use a Dante virtual sound card to help alleviate some hardware as well. But, if you're not using LTC, your sync isn't going to happen which defeats the entire purpose of this setup.
Also to be in sync, you will need a Quadro series GPU in each machine. And don't forget to add the Sync card in with a black burst generator driving the clocks.
Just running number's in my head:
$2k per GPU (RTX5000) x's 20 GPU's: $40,000
$1.2k per PC to house the GPU x's 20: $24,000
$1k per Sync Card x's 20: $20,000
$955 per Resolume key x's 20: $19,100
Total in PC hardware: $103,100
So not including shipping, tax, cables(fiber), fiber converters, content, labor cost, projectors, lenses, projection canvases, power, etc, you're just looking at over $100k in PC components alone to make this happen.
Does this seem like a realistic goal to approach for you and your client?
Again, you will need all of your content to be in sync using LTC and all clips fired via something like OSC.
This means no one can just roll in with a laptop and play on your system or nothing will be in sync.
Going back to my original question... Does it have to be 4k per projector? If you can get away with 1080p, thing just got a LOT cheaper! You can now use multi out SDI cards with a black burst for sync and use 3G-SDI for projectors and cabling
Or if nothing needs to be in sync (and you'll get screen tearing) just use a bunch of 3G-sdi and content that works for out of sync screens)
30 per side seems a bit excessive IMO.
Here's the Mirage in NY, from an after party of a festival I worked a few years back. They are doing about 4-5 projectors per side and is being driven from a Touch system that about 3 people know how to use, BUT it allows for integration from other users, which is a big thing. and since the canvas is so wide, most people just duplicate their outputs. Also, they aren't using 4K