I use 1/4" to 1/2" cubes when dicing. Wash times are longer this way than using a potato ricer due to the lower surface area.
Effectively, ammonia in an emulsion churns the iodide to the surface of the grain, or at least distributes it more evenly in the grain than otherwise, and this raises speed. It can also raise fog. There are other ways to improve the emulsion making than either method, but iodide does help speed a bit in the emulsion you describe. I have not read the formula for quite a while.
DO NOT USE DICHROMATE FOR HARDENING!!!!
Use either of the following, formalin, chrome alum or glyoxal.
I use the latter two at the rate of about 5 ml of a 10% solution for every 100 ml of 10% gelatin. You have to adjust accordingly. On film support, these will take about 24 hours to harden, but on paper support it will tak about 4 hours to harden.
On film support you will see an ISO speed of 3 - 6 if you are lucky, but if you coat on paper support and make paper negatives, it will probably have an ISO speed of up to 25 due to multiple internal reflections from the backing paper, and it will be less sharp. The speed will depend on laydown on both film and paper, and on paper it will also depend on the nature of the back reflection.