Thank you for participating in the forum. In many areas of the country ICE is offering DSL broadband with speeds up to 4 mbps. So if you limit yourself to areas where this service is already established you will find it to be fast enough I believe.
Most expats find the schools here excellent and you might consider giving your child (or children) the opportunity to interact with Tico students too. Here are some schools that have web sites.
Costa Rica Links - Schools Many other excellent schools exist, in price ranges from $ 200 per month to $10,000 per year. Private schools here are either on the US calendar (August to May) or on the Costa Rican calendar (February to December). This will matter if you are only in the country for a year or two.