Get a 4 silver, it has the best value combination.
It can be used for all sorts I have used it for Flyboarding, Snowboarding, mountain biking, larking about in the pool, swimming under waterfalls, walking around temples and so on.
It is very versatile and has a screen on the back.
The session has an internal battery, this is quite limiting unless it is the secondary camera.
Buy a decent branded memory card and you won’t have issues.
Accessories wise
Chest mount
Go-pole
floating bobber handle thing
Helmet side mount
Helmet Ninja mount
mini gorilla pod style tripod
spare batteries and charger
spare memory card, I changed mine out halfway through my recent trip to Bali just to make sure worst case I lost half not all the footage.
hope that helps.