Pick a realtor and stick with them. They will be your best asset in a home search and in the purchase process. An Asheville or Hendersonville Realtor can easily cover you in both areas but I would recommend dealing with a Brevard Realtor in Brevard. Even if a Realtor from Asheville says they cover that area, the reality is that they most likely rarely or if ever go to Brevard and will not know some of the zoning or other issues going on. Work with someone local to your area of interest. That's always the best thing to do.
Also read up on Buyers agency:
http://www.susanmyoung.com/WorkingwAgentsBrochure.pdf
A realtor that you are working with should present this to you on first substantial contact. They may also ask you to sign a Buyers Agency Agreement to firm up your relationship. Be careful what you sign! When I work with a buyer the first few times I will ask them to sign the agreement only for houses that I am showing them. Some realtors will have you sign the agreement for all of WNC. Then you are stuck working exclusively with them and you may decide shortly after that you don't want to work with them. I don't believe a full Buyers Agency should be signed until both parties get to know each other. Until then, it should be on house by house basis. Yes, that's an option.