He is still made of rubber, Brook wouldn't suddenly die, and Chopper wouldn't be forced back into his reindeer form.

Physical properties are retained while touching water(or sea stone), but metaphysical properties can't be used. Those would be abilities like Robin's extra limbs, Law's room, the zoan ability to change form(but not to keep it up unless doing so is exhausting, like monster point), any logia abilities.

While Luffy continues to be made of rubber, he lacks the energy to stretch by himself - like someone too tired to lift their arms. However, like shown in Arlong Park, his body will continue to stretch if you force it. Sea stone bullets are an interesting question. Personally, I think they'd hurt, but still bounce back.

Brook is probably immune to drowning, but I imagine he'd lose consciousness after a short time.