1. Servers racks are standard form factor, but you will need rails on the equipment you have to be able to mount them properly. If you don't have rack mount servers, you are sort of out of luck there.
2. Switches, UPS, etc can all be ordered to be rack mounted, but again it just depends on what you've got. Consumer switches and UPS are generally not going to have a rack mounting option. You can order shelves that mount into a rack cabinet, and put whatever you want on it, but that sorta defeats the purpose. I would just put the your extra equipment in the ikea device.
3. Racks vary a great deal in cost, I don't have much experience with anything other then Dell ones so can't say to much on others.
Most rack systems have a rack mountable KVM also. This helps with clutter and wiring since you only need one keyboard/video(monitor)/mouse for all servers housed in that rack. Some of the newer kvm's have a built in LCD monitor and they look like laptops. Just slide the kvm out of the rack and flip the lid up - instant kvm and LCD monitor/display.