you could build a PC that costs a lot less and still run 4 monitors.

One Issue on building your own machine is you will need to provide the OS. Linux is free but if you want Windows make sure it is in your budget.
When you buy one from an OEM like that, they provide it for you with a bunch of other unnecessary software. :(

Depending upon your software needs to run the applications you want, or the hardware components you want to include, then it is do you have enough hard drive space & proper back up area.

It does not matter if you buy today's top of the line or a few years old top of the line, you can get similar performance, the issue is internal parts in the future will eventually get cheaper & be of different standards than they are today. While you can put an SSD in any device now, you can't put DDR5 RAM in a DDR3 machine, and same for CPU's

My recommendation, is find a cheaper RIG, put in a good quality low noise 4 output video card set up for it, and use remaining budget on the monitors or keyboard, SSD's a back up drive and stuff of that nature. You can always change the case and style it how you like, but first you need to know the software & applications you want to use and what it will take to operate all of that effectivly.

All you need is an i7 CPU or better and 4-8 GB of ram, everything else is optional depending upon the work you want the machine to do.