I would certainly avoid marine paint as it's up to 90% lead. That will be a big problem for chickens. Latex can be very durable as long as you don't have a moisture problem. There are paints that are completely non-toxic out there, even some made from milk protein rather than oil or latex...
The floor is strictly a choice. A dirt floor would allow better drainage if there are spills, while concrete would assure a more sanitary bedding, reducing the danger of anaerobic bacteria and insects that could convey disease.
I won't tell you what you should do, but I would choose a dirt...