Sorry, haven't been there in quite awhile. But I have friends who have been.
My experience is west (Pacific) coast and Arenal (sp?) volcano. It was an awesome place back when, but heard it was more built up. Better for traveling with a family now I think.
Only surfing and fishing advice, no diving. Arenal volcano trip is awesome. Be prepared for cooler temps. You'll literally feel as though you're in an other country. East coast is more tropical (rain forest). Port Limon is kinda skechy as far as safety. I'm sure you'd be safe, but....just a heads up.
If you can fly into Liberia (west coast), I would. And bypass San Jose. If not no worries. If you need to stay in San Jose for any reason, better to stay in Alajuela. Just a tad north.
Good Luck in the travel, the locals are awesome people! Beautiful country!