Whether or not to use a mag plate depends on the size of the emulsion batch and/or just how good a vortex you can keep going as you ramp up the size. Different models seem to have different capacities. I feel that a 400 ml beaker 2/3 full is pretty much the top end of mine. Any bigger than that and I'd need an additional overhead stirring tool. My darkroom is too small to coat much more than about 250 ml of emulsion at a time anyway. Paper emulsion goes a long way. And, once you get a little practice, it goes fast. I coated twelve 9"x11" sheets last night in one hour from dry chemicals to coated paper hanging to dry. I just had to remember to bloom my gelatin ahead of time. Since practice is an important part of the game, I strongly suggest you make frequent, small batches rather than honkin' big ones. (Saves on silver costs, too, when the inevitable Big Fail happens )
If you really want to make huge batches, you'll need to test your stirrer's capacity. Make a plain gelatin solution that is about the thickness of very heavy cream when it's at 45-50C. At any amount you go with, you'll need to see a good, strong vortex that is visibly moving the liquid at the beaker interface. In other words, you don't want any dead zones. This is critical, but not complicated. Any tool or mixing contraption that keeps the salted gelatin moving as you add the silver will do the trick.
Good luck and fun.