But how do I lower the tension? I think its just the friction in the tube.

It comes with 2 spinning tubes so it does spin freely

Welcome to the world of 3d printing

But doesn’t that create an offset weight? My part will probably spin at several thousand RPM.

Some addition to my post: The computer I found is a Fujitsu Esprimo Q957. I’ve read online that they are very power efficient and don’t draw as much. I will probably run some lightweight task almost 24/7 and sometimes heavier tasks for short periods of time. A raspberry pi is for me too expensive for the average specs, even if it is very efficient. I think a upgradable pc or mini pc is best, because they are cheap, but can be easily upgraded without buying a whole new computer.