65mm could be perfect in a good housing and with a properly sealed baffle.
The size of the holes really depends on your D/S gap and really shouldn't be any larger then double the D/S gap. For Stax that means 1mm or so given their 0.5mm D/S gap.
I for one don't like to damp much but I've gone to extreme lengths to dampen some drivers which just won't behave. That said, airdamping is IMO a very good idea as it it traps air next to the diaphragm and can stabilize it. Most undamped electrostatic drivers have some resonance frequency (usually in the upper midrange, lower treble) and this helps to tame it. Take a look at the picture below, that's a Stax SR-007Mk2 driver and notice the ring with no holes around the driver. That's still part of the stator with the diaphragm beneath it but it can't output any sound. The small Stax SR-003 portable headset goes even further where only a small part of the stators is open.
