I very much consider myself a wholesaler. I do not try to build inventory or carry names for years. I keep the names I want to build and sell the rest. If you look at my prices compared to others on the selling platforms mine are priced and mostly below their apparasial values.
I mostly have EMD (exact match domains), searched terms with a clear purpose. I think that is paramount for your business/site. If I'm looking through search results, or I see your business card...of they specialize in what I am looking for.
I get most of my data from estibot and wordtracker, more info on that when I finish my webite.