#1
I'm not sure if I should get an interace or just a regular cable with
USB on the end. I'm not in the need of any extra ports or something, just plugging the guitar in via USB.

Will it make a difference in sound if I just use a regular cable 1/4" TRS to USB cable?
#2
It's better to get something that can act as a preamp or the signal might not sound as good as you'd like.