Currently I have a Groove AC and a Routerboard hAP AC.

The Groove is currently set as a router, and the Routerboard is in bridge mode. Since I only use the Groove to pick up wifi (basically act as a wifi booster) and pass it on to the Routerboard, (to which all other devices are connected), should these be setup the other way around? i.e the Groove plugged into the Routerboard WAN port and set in 'bridge' mode, and the Routerboard set in 'router' mode.

Everything works just find as it is at the moment, but I have a sneaking suspicion that it's not quite best practice.

Personally, I would prefer to have the inside box as router, and external as "accessory".
CPU-wize they are identical, although box has more headroom: mem, storage, bandwidth.

But it's working now and you're on wifi, so won't be pushing gigabit speeds anyways. I would say adjust on next big reorg.

If the Groove is attached to a vehicle and you frequently need to find a new AP then I would leave the Groove as a Router. The hAP can be set as either a Router or a Bridge depending on your circumstances.