There are different types of paddling, including canoeing, SUP'ing, rafting, kayaking, which further includes touring in long boats (the kayaks are 12, 13, or 14 feet long), white water, which itself is further broken down into play-boating and/or creeking (boats are 5, 6, or 7 feet long). The longer the boat, the more stable. The shorter, the more mobile. This makes a difference depending on the body of water you're paddling in, from lakes to running water. And water volume and flow will also impact the boat you select. Across these boats, there are a variety of differences that impact your experience, from the channels on your hull to the way you're positioned (sit on tops vs. fishing boats).
Lightweight merino wool or cotton baselayer. Baselayers are the tops closest to your skin.
Shorts. Wicking. Spandex, cotton are OK great.
None. But, also, water shoes.
Change of clothes and dry bags (to stow your clothes and towel. All dry bags float, however some are made from sturdier materials and will last you longer.)
Most lakes and rivers where boating is permitted will have a rental shop for boats and paddles. nearby. However, if you're going to buy, here's what to consider: length of boat. Weight of boat (there's this thing called ferrying where you carry your kayak to the next put-in and that really sucks with a heavy boat). And cockpit size relative to your own weight and height. You're going to be sitting in this cockpit for hours and hours, so the more comfortable, the better. And don't forget your car rack.