Allot of these sorts of places have small worshiping areas, with bronze statues of their Gods, and Candles for worship, and achieving enlightenment (or what ever.) Plus Racks that holds Swords, and wooden poles for sparing, and practice.
Plus perhaps, small ornamental vases, and other decorations.
Maybe big raised Basins, that hold water so the Dojo can stay hydrated during his long worships, and physically draining practice sessions.
What you have so far looks pretty good. You could probably do a search for ideas on what to include in the room.
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"Your weapons are no match for ours! People of Mars, surrender!"
"Um, this isn't Mars. This is Earth."
"Earth? Earth-with-nuclear-weapons Earth?"
"Yes."
[long pause] "Friend!!"