#[4] will have some good advice for sure. In my experience, the all inclusive resorts are in Guanacaste, in the northwest of the country. There is an international airport in the city of Liberia just for this reason. The best time of year would be dry season, which is something like December to April. Rainy season can be ok though, as in nice mornings with rain starting in mid afternoon. The sun comes up around 5:30am and goes down around 6pm all year, so it is an early wake and early to bed vibe anyway.

Enjoy!