Concerning the number of available player slots, try to check the menu you can enter by using Ctrl+R in the map editor. On the right side you determine how many players should be available. This number is indeed not linked to the number of starting points. Don't know why's that. After you set slot 5 to 8 to "empty" (or what it is called) you will get a 4-player-map.
Maybe number 2 is solved after that, too.
Hope, it helped. Good luck and enjoy map-making!
