Your agent can assist you in finding homes and the information you need to make a flood determination that you can live with. The same goes for the septic systems. A purchase contract of any home, no matter what community, that has a septic system should contain a contingency in the purchase agreement that you have the right to have an inspection of that system. If it needs replacement, that can be worked out with the seller prior to closing.
As to rising sea levels? Well, to be honest i am not qualified to comment on that. That would need an expert in that field.