lets go back to the start :-

Do you have a working system now ?
could you give us the specs of that ? if we know where we are starting from, it is easier to give advice .......

As you want to upgrade your CPU / Mo-Bo / GPU then as the duck has said, it may be easier to just get an entire new system, and keep the first one for your [just started] network

you WILL need to consider a PSU [power supply unit] too, DO NOT go the cheap route here ....

go to a supplier site, and 'build' your dream box only, add the cost of KVM kit [keyboard / video / mouse] to the total, and see what you come up with, if this is in reach, then it might be the better deal ..........