I suggest a rough pass on the map at first to get started. Basically do an "ehhh maybe that sucks but it's okay for now" attempt at all aspects of the map. Divide the map area with terrain, place things approximately where they should be, add a couple doodads so your eyes don't hurt but don't worry about that stuff, rudimentary units with generic abilities, the most basic triggers to get essential functionality going even if it leaks or is laggy or sucks, and anything else that occurs to you. But don't get bogged down in the details: think broad strokes!
Hopefully this allows you to see your map's potential as a finished idea. With this rough sketch you can then focus efforts in a specific area for a while and not feel like you have no idea of the bigger picture of your map and if you're wasting time.