Tower defense type game

I was looking at the tower defense starter kit and I was wondering how hard would it be to have a number of castles scatterd around a map that the player has to protect instead of just one??

Also how hard would it be to have spawners that would spawn projectiles randomly during a wave aimed at different one of ones cities.

basically these missile projectiles would be the monsters so instead of having preplaned travel paths projectiles could come from any direction from the edge of map spawners..

I have a number of finished and textured meshes for cities to use instead of castle and also defense towers and missiles to represent the missiles incoming… would anyone be interested in working with me on this?