For a reference point on chainring sizes, consider that a typical road double crank uses a 39T small ring. A "compact" double will run a 34T. Triple cranks usually have a 30T inner. If you've ever rode a bike with 2x or 3x gearing, you probably have a good idea of what those small ring sizes feel like.

I don't know how steep the hills are on the Cornish coast (sounds awesome, by the way), but if it were me I would probably try a 36T, which would still get you some reasonable top-speed gearing (around 26mph at 100rpm cadence) but also give you a really low 36x42 combo to get up steep hills.

It just depends on how low you want to go, and how much you're willing to give up on the top end.