Building fitness to start surfing through swim workouts

I want to start taking surf lessons in the near future, but first I know I need to build a base level of fitness and stamina. I've taken a few lessons in the past, and I only lasted about 10-20 minutes in the ocean popping up halfway to my knees, so i want to make sure next time I last for an entire lesson. I haven't been swimming laps lately, but I'm about to start again, and I also do pushups a couple times a week (I'm up to 80 pushups broken up into five sets). I've been doing swim workouts of about 1650-1750 yards, and I occasionally worked in sets where I did 50 yard reps breathing once every 4 or 6 strokes.
My question is, is doing sets where I breath less often like that a good way to build my fitness and stamina for surfing (along with other ways, of course)? If it is, would it be a good idea to step it up and sometimes swim laps where I breathe once every 8 or even 10 strokes?
Also, is swimming that many yards per session enough as far as swimming to build the kind of stamina and endurance needed for surfing? If not, how many yards should I eventually increase that to?
My question is, is doing sets where I breath less often like that a good way to build my fitness and stamina for surfing (along with other ways, of course)? If it is, would it be a good idea to step it up and sometimes swim laps where I breathe once every 8 or even 10 strokes?
Also, is swimming that many yards per session enough as far as swimming to build the kind of stamina and endurance needed for surfing? If not, how many yards should I eventually increase that to?