The diving centre provides you with a life jacket for any activity, if you want one or if you tell them you can't swim. While I can swim, I still took one coz I figured if I were to fall out of the kayak, I could spend little to no energy by floating to my heart's content.
The first time in the kayak felt as if I would fall out, but I soon got the feel of it and by the 6th day (yes, I went kayaking every day) I was fine as I had adapted to the rocking motion. The waters were so placid and calm, and the area kayaking was not at all deep so I had no fear.

You will be fine.

On your way back, give yourself time as there are two security checks. One to get you in the terminal for check - in and one when you go upstairs to clear immigration before being able to get to the gate. There are separate queues for business class pax, and you may be fortunate like me to get from boat drop off to lounge in under 40 mins.

There is just one lounge used by all airlines. IRRC, it is called the Lelani lounge and it is just to the right of the elevators that take you down to the departure gates.