Dutch,
You asked some really good questions and some that have already been covered extensively elsewhere. Since you're a newbie in the newbie section AND a fellow whorticulturist

, I have to cut you some slack, however I do recommend you venture out of this section and look around as you should be able to find the answers to probably most of your own questions.
Here is a link to a recent thread right here in the newbie section by jenjad which covered the subject of internet cafes
http://www.costaricaticas.com/phpBB2/viewtopic.php?t=6942. Basically, yes there are plenty of them out there, they're dirt cheap and several of the most conveniently placed ones are indicated on my map. There are also free wireless networks in several of the downtown hotels and free public computers in the lobbies of several more. There is even free wireless internet at the airport when you arrive and a computer w/internet that is free to use for customers in the Zona Blue and one can call the US toll free from there using VOIP. Here is another good thread on laptops
http://www.costaricaticas.com/phpBB2/viewtopic.php?p=47579 and internet access
http://www.costaricaticas.com/phpBB2/viewtopic.php?t=5944.
There are both pros and cons to bringing your own pc vs. using the internet cafes, but for most
shortterm visitors, my recommendation would be to seriously consider leaving the laptop home since the internet cafe alternatives are both convenient and cheap. OTOH, if anyone does decide to bring their laptop, there are plenty of places to connect through wireless. However your situation is a little different. First of all, I happen to know you're planning an extended trip with an eye to eventual relocation to CR. Second, you mentioned you had a mac. Unfortunately, though I suspect it will work fine there, personally I can't say that with absolute certainty, not being a Mac person. I'm sure others can chime in with the correct facts on that very good question. Finally, bringing your own cable modem from home (even if it would work on RACSA's system, which AGAIN I'm not sure about) for a short visit is simply not practical and you can expect to have to wait a long time to have RACSA hook you up once you do move here.