I'm gonna have to agree with KENIKE, I've been to the North Coast at least three times (always Late November) and have had ok surf. I agree that Witch's makes that area attractive, but I've never made the effort to put a trip together to get up there. From what I've heard it can be fickel, and it's a commitment to get to it, it is remote!
Jaco/Hermosa has some the best surf going from my experience. Hermosa really works well on a South, but will usually has some pretty decent surf regardless. Jaco/Hermosa offers a lot of different waves, Heavy Hollow beachbreakes, Roco Loco, which can be mind blowing! Surf it with someone who know's it, and Jaco is a safe bet if Hermosa is too heavy.
Diving ??? I've gone diving in Playa Coco years ago and it was fair at best. The visibility on the Pacific side is not all that great, 20ft at best when I was there.
Good luck, post some pics when you get back. If you're doing the surfcamp thing, check out Loma Del mar, I worked there for a couple of months about 5 years ago, Richard Garrison runs the place and he's a pretty good guy, will get you to beach before sunrise everyday, and depending if the boat is working can get you to Escon if it's working.
Good Luck!