It is needed since it provides a frame work to level everything out from what I can see. There are better ways to do it, but you need either a welder or mill for that to work.
The reason why a MDF board would be a hazard to your lungs is because of the types of resin they use to hold everything together. When heated it would start off gassing.
If you are really worried there are places where you can either order one that is glass, metal or acrylic, or even just regular wood.
If you are handing with a band saw and a file. You can make your own it is really easy. If not order it and save your fingers.