I don't have expert knowledge on how a tile and marble installation business would do here in Southeastern NC, but here are some online resources you can check out to research the business climate in the area.
Business Directory: Click search business by category drop down menu and select flooring. This will give you a list of flooring businesses in the area.
Wilmington Business Resources
Wilmington Business Relocation
Wilmington Fast Facts
Wilmington Demographic Statistics
Wilmington Cost of Living
North Carolina State Statistics
I hope this helps. Also, you mentioned Carolina Beach. For now, building has slowed down dramatically in Carolina Beach. Only a handful of homes sell each month in Carolina and Kure Beach. In 2004 and 2005, Carolina Beach experienced an extreme sellers market with an over abundance of speculative flipping and building. There are many beautiful new homes that were built in 2005 that still have not sold. So, I would think this would be an area that would be a bit repressed for contract work. Leland and Brunswick county continues to see development.