would it be a problem if i had my phone on a different plan than my laptop?

Cellular plans only affect the network connectity of the phone, not the computer. While the cell phone can share its data plan and uses the data transfer in a hotspot configuration, it is not conveying any manner of the hotspot except the data, not the actual plan. And the data is relayed over WiFi, not cellular.

If you want to get a USB Cellular dongle for your laptop using a different plan, that's doable.

And that way your cell phone does not need to be used a relay for the Mac.