No: the outings take place in sheltered waters, with an initial briefing and a guide who adapts the pace to the group. All you need is basic fitness and to be able to swim at a basic level.
Almost always yes: mask, fins, kayak or board and life jacket are provided by the operator. If you prefer you can bring your own mask; a wetsuit is only needed at the start and end of the season.
From late May to September. June offers the best visibility; August the warmest water. Early morning outings have calmer sea and quieter seabeds.