frank,
The Placencia peninsula has the largest marinas with associated condo/townhouse developments, on the lagoon side. I know there is one at Roberts Grove, but there are others there as well. There are a number of condo developments and also some property that is being developed where you can build your own home, on the marina side, and keep your boat in a slip there.
Boris Mannsfeld Associates works with Pathfinders in Placencia and he is part owner of the marina development at Roberts Grove.
It’s always a good idea not to buy on your first trip. You can also rent a house in the marinas. I met a couple who does rent at the Roberts Grove marina. If you rent first and talk to expats who live on the Placencia Peninsula you will hear the pros and cons of the various marinas and properties. Then you can make a better informed decision.