Well, as a typical Costa Rican, I have been there dozens of times through my whole life, hehehehe.
First of all, if the estate is on the beach, then you are not really going to Liberia, since there are no beaches there. Liberia is the capital city of the province of Guanacaste, and it is home to the Daniel Oduber International airport. It would be nice know to which beach you are going, so as to give you advice on which places to visit nearby...
Weather in Guanacaste is hot and drier than in the rest of the country. Rain is always a thing to consider. Get tons of mosquito repellent and sun lotion. Try to avoid long exposure to the sun, specially between 11.30 and 15.30, that's the period of time when the UV intesity is the highest.
Guanacaste is a beautiful place, and it is no wonder that many American and European millionaire have chosen the region for their retirement. Paradisiac beaches, hot weather, it is a really beautiful place to visit. As for safety, it is a very safe place to visit but common sense should be observed, specially if you are going to be going around the place with expensive photographic equipment (for example, don't leave a laptop bag on your car).