Your perforated metal sheet looks good. I'm sure either one will work just fine. Please be sure that the metal sheet still has very good insulation.
What would you use for your spacers?
The headphones with Arnaud now are my version 1, Jacklin Float style headphones. The spacer is 0.6 mm, and yes, they require a bit more powerful amp than Stax headphones.
If you want to build your own amp, I highly recommend you build a KGSSHV. It's...