Bali is great place if you know where to go. If you get lost, it can be really annoying :D So if you don't have much time, I suggest to get a driver or guide, depending on what you want to do. I've been surfing in Indonesia for while and can only say if you want to learn to surf or improve you beginner skills, you should hang out with a local. They know where to go and are fairly cheap, compared to let's say a european surf guide. Kuta is a good beginner beach but if you have a good guide, they take you around the island for best and less crowded surf session. Just tell them you don't want crowds ;)
I found the surf schools in Bali from this site very helpful. They do guiding and also offer accomodation if you need it. Definitely recommend trying SUP with the Priority SUP School Bali. They are simply the best (I think also the only ones) and do great tours through the mangrooves.
Snorkelling is best on Nusa Lembogan, you can take a ferry or fast boat from Sanur for a fair price. There are plenty of places to sleep along the beach and they organise you a boat driver for snorkelling. This is almost a must, if you want to do snorkeling in and around Bali. If you check accomodation on booking.com you'll find plenty. I personally like the Song Bintang Villas.
Hope this helps and enjoy your trip!