If you want to play 4-player free for all, the easiest way to do this is to have 2 sets of the game. If at least 2 people in your foursome own the game, you can readily do this.
This would ensure plenty of spells, markers, etc. Put the 2 boards together to form a 4x6 grid. A 4x6 grid is PERFECT for 4-player free for all. Enough room for each player to establish a small base of operations and not be too close to the next player so there is some time to react before being rushed.
Where do players start? If you number the 24 zones from left to right, top to bottom, with 6 zones across, and 4 rows of zones tall, the starting positions are: 1, 5, 20, and 24. Or, try 3,12,13, and 22.
The only problem with 2 sets is that there are only 2 player colors. You can use pennies or tokens for action markers for 2 of the Mages. A 4-player set with green/purple will be available for purchase this fall.