wow a lot for you to consider, ticket to ride has a pretty well established program and a volunteer section too, the prices are reasonable.
I have some things for you to consider.
A group of backpackers arriving in a third world country without locally based infrastructure to support their arrival is extremely problematic.
The community may not be able to support a group arrival enmass, also you as a group are at risk of crime if no local look out is there for you!
Most successful surf travel of any sort usually has a strong representation of local people benefiting from the surfers and knowing the local customs.
You would need to have qualified surf lifeguards and first aiders among your group,
I see you are considering taking a 12 week surfing instructor course, that is no way near giving enough experience for this.
If you organise something like this , you are the one liable for the wellbeing of your travel friends and also responsible to the community you enter, for your group's behaviour. (it's taken very seriously in most third world countries ).
Will you have the structure to protect the entire group if one member breaks the law
As for volunteering to pay your expenses, do you really know how poor some of these areas are
You will note that Ticket to ride has the volunteers paying to stay and help, not having the local community pay in money or kind to have a volunteer..
I really respectfully and kindly suggest that you have a really good plan to cover all this and more before you go.
I have traveled to many many out of the way places with Rotary and other NGO to aid first and surf after, there is nothing better than helping this way, but have a strong clear structure behind you, it is just too risky otherwise.
If you go as an individual the course is entirely different, if you relate well to people and are flexible then so many amazing opportunities arise to both help and experience!
My thoughts and advice would be, go as an individual, get to know where to go. know the locals and then build your idea on that ( after all that's how most surf travel companies started)
It's a nice rose coloured glasses idea, it has a chance of being a genuine goer but, not without a lot more work and forethought.
Finally as a buyer of a trip like that I would be seriously interested in the experience of the organiser and their backing credentials gained over some longer time.
I've taken up troll hunting just for fun, instead of a rifle I'll just use a pun! 冲浪爷爷