I don't know of trip planning resources; I just research the hell out of everything I do, so my trip planning resources are "all of the internet."
I have been to Costa Rica several times, though, and am happy to help as you go along. I'd recommend getting a VRBO in each of two areas: (1) the Arenal volcano and Monteverde cloud forest area (I assume Arenal is what you are referring to, but it is active, not dormant), and (2) the beach areas of Tamarindo/Playa Langosta. I actually prefer the latter area, but the former is probably the biggest tourist attraction and is a must-do as well if you haven't done a lot of volcanos and rainforests. Theoretically you could stay in one location and just visit the other, but you'd be doing a lot of traveling; they might look close but are well over three hours apart as the roads in Costa Rica are surprisingly bad. So I strongly recommend spending a few days in each of the locations. It's all gorgeous.
Once you decide where you're going, I can help with specific recommendations if you'd like. I also have rented houses in the Tamarindo several times through VRBO or otherwise. Oh, and no matter what, fly into Liberia, not San Jose. Much easier and safer.