But you must consider the fact that emulsions of 400 - 500 ml and bigger are quite large and you probably don't need to do them unless you are going to "mass produce" some film&paper. It's better to do small batches, then you waste less chemicals when you search for the good procedures. 200 ml of emulsion coats a huge number of sheets, and this amount is not a problem for a magnetic stirrer. Magnetic stirrer at least ensures proper mixing at the bottom. We have really had no mixing problems with a magnetic stirrer. Our batch size is 150...200 ml and we use glass beaker.
During the critical precipitation the gelatin level is not so high, so the viscosity doesn't seem to be a problem either.