Thanks to everyone who has taken the time to respond so far and there is some great advice in there and locations that sound right up our street.
On the subject of car rental what we usually do in the Caribbean is take local buses everywhere - we're wanderers rather than go toers - in the hope of coming across that nice beach bar with long,boozy lunch written all over it.
But if we find somewhere we'd like to visit then we'll hire the cheapest wheels we can find for a day or two.And avoid the booze !
Are the buses into the French side timetabled or is it just a question of flagging one down when you see one near a bus stop ?
We're staying not far from the Horny Toad so obviously we can see from the maps there are plenty of bars and eateries within walking distance.
To get to Maho on foot Google Maps is sending us around the runway on the airport road - is it possible to simply walk there on the sand along Simpson Bay Beach ?
Once again thanks for everyone's input so far and please keep any suggestions coming, especially on the margaritas ...