Hi Dave, the biggest holiday of the year on the coast is Semana Santa… the week (maybe even two weeks) before Easter. Don’t know when that falls this year, but you will find hotels booked and beach towns CRAZY full of people — I would avoid that time at all costs.
Montanita would be my pick for a place to go to a surf camp — you might want to check this one out: http://balsasurfcamp.com/en/
Also, I’d suggest you email my friend Pete Stromberg in Canoa — his email is pete@canoathrills.com and his website is http://www.canoathrills.com/ — Canoa is another of the best surfing towns on the coast.
Have fun!
P.S. Once you decide where you are going, check on local holidays in the area. Every town in Ecuador seems to have some kind of holiday or festival every month or so…