Load isn't an issue here and the amp will run just fine without one. No need to turn down the volume when switching headphones but some are less/more sensitive then others so beware of that.
The bias is 580V and no need to alter anything here. It will drive any of the high bias headphones just fine like that. The modern Stax headphones do not need the dustcover but something like the Sennheiser HE60 needs one.
If you have any specific questions then just PM me ohh and welcome to the mafia.