im' kinda new in diy so im easily impressed but those are awsome!!!
Your understanding is correct. The only thing that I will add to your drawing is that I glue the dust cover on a 1mm spacer.
I coat only one side of the diaphragm that is the one facing the ear. The bias voltage now is at 570V which is similar to what Stax is using.
There have been some experiments done by other DIYers that show no noticable difference between coating one side versus 2 sides. I didn't bother to try it.
I always glue the diaphragm to only one of the spacers. The other spacer is used as a charge ring for the diaphragm.
About the diaphragm size, if you are going to make a pair of full size, over the ears headphones, go for the biggest diaphragm size you can make. To achieve good low frequency response, you need a large diaphragm area. Diaphragm diameter of 40 mm won't give you good bass.
I don't know anything about SR-001 type headphones. I've never listen to them.
Please feel free to ask anything you like. I don't mind at all.
I have been using a 3 pins XLR connector for my mono prototype. Although this is not respecting the XLR's datasheet I am not sure it is an actual issue. On a related thought, as anyone found male stax plug ? I still have the female sockets Franck Cooter gave away but can't match it yet ...