There's a couple of things to think about. Flood insurance is provided by the federal government through FEMA and the NFIP. Unless you go through a private company, you will not have the same kinds of coverage via NFIP as you would a traditional policy. There is much less coverage for the policies.
- Rebuilding your home: up to $250,000 in coverage
- Personal property: $100,000
- Additional living expenses: $0
- Coverage to other structures: $0.
Because of this, you should think twice about building a home in a flood plain. Regardless of how much property you actually have, the maximum amount you will receive is listed above. As for your second question, I'm not an expert in dwellings and thus do not feel comfortable answering that question. I would speak to a contractor.