Best used MacBook for dedicated tethering?

I've been using my only MacBook (2016, Pro, 13") for tethering w/ C1. I'd like to get something used and fairly inexpensive that I can leave setup in the studio for this. I'm assuming, perhaps incorrectly, that a lot of memory and power is not too critical for this purpose? Part of me thinks that a higher quality 13" image would be better than a lessor quality 15" image.

I'm also thinking that maybe a used iMac wouldn't be a terrible idea and might actually be more bang for my buck. This might require a cart or something other than the old c-stand w/ plywood top I've been sticking my MacBook on.

Any recommendations would be greatly appreciated.