Geezer has been on the money with advice for you, you will need to consider Indo visas as longer than 30 days needs pre approval and a little more upfront cash. The old way was a day trip to Kuala Lumpar or Singapore and then re entry
As you are doing gap year you are young enough to get good insurance, most camps have it as mandatory.
Consider too medical vaccinations tropical,diseases and malaria prevention, White English flesh is a mossie magnet!
Dengue typhoid typhus are considerations, controversial. but I would up to date on Covid vaccination too.
This applies to any tropical or subtropical surf zone, believe me the further you get from mega crowding the more prevalent the nasty bugs.
Where you are looking in is Sumatra is and the camps within budget, a range of good spots nearby , car trips along the coast won’t happen as to get to each surf area you have go up into the mountain spine and follow the next river down to the next coast area. Adventurous yep, cranks up the expenses.
The further out too, the more sketchy the internet connections become.
A flying within Indo, try to stick to Garuda, some of the other airlines are riskier.
Indonesians of all faiths are welcoming and if you enjoy interaction and learn to speak Bahasa Indonesian reasonably well and use smiles and respect you will go a long way.
A book I recommend is Indo Lingo and Surf by the late Peter Neely, has a wealth of surf spots and how and when they work best.
Also basic conversational and how to barter conversationally.
You need to self sufficient in safety in the surf, there are absolutely no life saving services, less so and the surf is generated on storm systems in the south of the Indian Ocean so swell trains can arrive suddenly jumping the surf suddenly, thankfully there is much better prediction available now than when I first went to Indonesia in 1979. Ouch that ages me!
Bear in mind too the Sumatera end of Indonesia is Muslim so respect manners and modesty are the norm!
You will be challenged in the surf, the waves are not lazy like the UK they move faster for paddling and pitching their faces, your surfing will improve greatly!

I've taken up troll hunting just for fun, instead of a rifle I'll just use a pun! 冲浪爷爷