Themes are a very literal interpretation of a style, and often appears juvenile and kitschy. What you need to do is find the essence of the theme what draws you to that theme, what feelings does it evoke and how does it make you feel.
Coastal is another style that evoke very specific feelings this style is often misconstrued. Instead of literally choosing everything to recreate a beach, why not think beyond that. When I think coastal I think of the Cape, Newport or the Hamptons. I think crisp, cotton fabrics, relaxed, casual furniture. The colors would be calming but not boring....refreshing greys, taupes, seaglass blue and aqua greens. The introducing of natural texture, sisals and colorful ceramics.