I'd start with researching video walls. https://en.wikipedia.org/wiki/Video_wall seems a start.
I don't think that I need much data storage for this project. 500 GB is probably enough. So if I could just slap together enough RAM, CPU, Graphics Cards, and monitors, that would be great.
I don't care how this looks at all. It can look like a scrap heap on a cat scratch pole for all I care. I just don't want a lot of useless parts on it like too much Hard Drive, too much Mother Board, Power Supplies, Cases, Disc Drives or whatever else is useless to my cause.
I want 8-9 monitors to light up on the tree all at once with only one power switch to compute Wall St. trading software and charts. This doesn't need to be the monster truck behemoth gamer rigs or nothing heavy duty like that with airplane props blowing and police infrared scanners flying over head looking for hydroponic growers because the electric bills are so high.
I want this to be strong without any lag, but I don't want to waste a lot of electricity since it's going to be on all of the time.
Cheap and smart. That's all.
Last but not least I want this to be as cheap as possible from Ebay, Craigslist, computer recyclers/junkyards and similar. This is my personal "learn how to make computer frankensteins for absolute cheap as possible" project for me, and I may make a video about it, so other people can do the same. With so many people out of work, this may be something helpful to some good families out there, and I'll become a better Computer Jedi Knight so to speak.