Total players should be up to 4 only, the idea of adding a player from top and a bottom feature is disastrous, those players would risky fight there way for expansion, creep outs and territory harvesting they will just end up loosing unless played in 1v1 matches. Though this can be considerate for a team based, still the idea of no expansion for the top and bottom players is daunting.
Much of my explanations about expansion, the map is filled with goldmines, no much goblin labs, taverns, and even merchants in sight the game would be very unstable to finish.
I would suggest you remove 2 players, add neutral buildings and adjust much of the terrain or map size.