Kerala is known as Gods own country. Though May has scorching heat, still evenings are cool due to a short downpour. Will share a few things you might want to explore Kerala in May, see if it is suitable for your travel. Visiting Mullakkal temple for architecture in Alleppey
Enjoying view of banasura hill Wayanad
Shouting to hear your voice back at Echo point Munnar
Enjoying flora view at Vandiperiyar thekkady
Watching and trying to touch the lovely waters of Thusharagiri falls Lakkidi. Best mode of transport within Kerala is renting a vehicle or booking a cab. Though bus services are available, easy mode of transport within the state is vehicle.
I travelled in September, while May sounds fine too. You may find occasional rain showers. The best way to move around is to rent a car. Either hire a self drive one or get one with a driver. Relying on public transport alone may not be the most optimal way if you plan to visit a couple of places.