Good luck on getting one soon. I ordered on the 4th of November, and very keen on seeing how well these machines work, currently looking into Game Controllers.
Wireless/Bluetooth - 8Bitdo SF30 Pro Controller or 8BitDo SN30 Pro+ Bluetooth Gamepad
I was very lucky... I ordered through Core Electronics and the first date was Jan, then Dec and in the end they got an order in Mid November - great service!
As I was saying FB I still can't get a build I am 100% happy with! Newer chips in the 400 seems to be causing a few issues.... But i'm sure they will all get there! A few people on the net seem to be doing their setup on the Pi4 - updating - and then transferring to the 400, sadly I don't have a Pi4 at present!
Manjaro seems to give the best overall performance as a base OS, no surprise as its Arch based but even their latest image did not have WiFi or Bluetooth with out and "unofficial" update I got from their forum!
Then Amiberry ran very quickly but I can't get it to boot to fullscreen - its been driving me mad - sadly not had the time to work on it as much as I would like! Ubuntu did work fullscreen but its got a very heavy GUI and not had the time to try an alternate desktop as yet! I'm sure Lubuntu would fly!
Controllers are a bit away for me yet...