I'd like to make games like Battle for Wesnoth - http://www.wesnoth.org/, or Advance Wars, which just doesnt seem possible with RTS pathfinding.
Why not? Give your objects some variables to specify whether or not it's their turn, and only move those objects on their turn.
As far as grid movement, just set all your waypoints and destinations to grid coordinates. If you need to get, say, a 32x32 grid coordinate for the mouse, you can do it with floor((mouseX / 32) * 32), floor((mouseY / 32) * 32).