If you are working up a shack installation, a desktop or small tower would be better because you will be able to add physical COM ports onto the motherboard to give you reliable COM ports to operate digital software that uses COM ports for PTT and or FSK keying. Not all products have CAT or CI-V rig control, but need a way to PTT the radio.
USB COM ports are virtual and can potentially "float" around to different COM port numbers if you attach and detach the associated device from your USB hub/ports. Software products have to be aligned with the COM port that your Rig is attached, such as Signalink, Rigblaster, or CAT/CI-V USB cable.
I prefer a soundcard that has LINE IN and LINE OUT jacks (usually in the back panel) LINE in is LINE LEVEL audio, which is compatible with LINE LEVEL output of some radio DATA OUT lines.
I am pretty sure you can install multiple sound cards in a PC to drive multiple radios, but I have not tried this myself.
If your radio has a sound card in it, that is VERY good way to go with digital modes. My ICOM 7200 has a soundcard and it makes it very easy to use... I run 1200 baud packet on my Yaesu 7900 dual bander using the soundcard inside the computer, no problem... but I did take care to ensure the lines between the radio and the sound card were electrically isolated by way of 600/600 ohm AF isolation transformers.
Good luck and 73's
Jeff KG5AHC