1) Most probably, a finished working map should load from the regular 'C:\Docu...\MyGames\...\CustomMaps' folder. Use as in Play with it? As long as starting locations are defined for any Major races possible, just click and select along while using it by its name in the provided setup field.
2) This process isn't a scenario, it's a simple map context. The game settings still perform as the main conditions by choice rather than the map itself.
3) Nope, that's some vertical gap ratios that randomizes textures on the 12 tiles width through steps. No.
4) I presume you mean the usual maximum of NINE opponents. Then, the answer would be no, sadly.