Is there any particular reason why you chose to do the reduction in three stages?
If you are looking to build a custom transmission with an end ratio of about 10:1, you can use COTS gears from AndyMark with only two stages using a 50:14 (3.571:1) reduction in the first stage and a 40:14 (2.857:1) reduction in the second stage, for an overall reduction of 10.202:1. And if you have access to a milling machine or lathe, it isn’t very difficult to lighten these gears with pockets and/or holes drilled through them.
Ya there was a reason, and it appears it was a wrong reason so I am probably going to switch it around. I usually use wmberg, their gears are expensive but their choices are great ant they are ammazingly precise.