fall can have some bigger surf being that its hurricane season and all, but if you talk to anyone who has been to the pacific coast they will tell you the surf is pretty consistant. We are in esterillos - which is about 15 minutes from Jaco. if you are serious shoot me an email/msg and maybe we can work something out.
I stayed in Tamarindo, rented a small SUV and traveled up and down the west coast during Dec-Jan. All spots were breaking consistently. As for boards, there's plenty of places to rent in Tamarindo. I actually saw the exact same Walden I left back in the states. Highlights were Witch's Rock, Avellanas, Playa Negra (heavy) and Playa Grande.