What a great spot! i’d drive around a look at other houses to get a sense if what you like - traditional, contemporary etc.. and then I’d find a fantastic residential architect to get you started

Hmmm….. home OR duplex. Decide what you want & hire an architect.

Hire a surveyor to find the legal lot lines. Check local regulations to see if you can have a duplex or if it must be a single-family home. Then check setback, hardscape coverage, and raised foundation (for ocean storm surge) regulations. Then hire an architect who works in your budget range.

An architect first stop.