I'm no expert in terms of OSM conventions, so I cannot tell if the primary name should be in Japanese or English. For the secondary name fields however I strongly prefer having both names available.
Regarding "official" translations - the Tesla website is my reference. Changing country from JP to any English speaking one will also change the name of the supercharger, and that should be the official name of the location. Note: Both names might change over time, especially when another SuC is built nearby.

Again, the navigation system in Tesla vehicles tells the driver about this, and there's plenty of notes, from small to large, from entry to exit that state the opening hours.
And since the official opening times of the supercharger coincide with those of the parking garage, even non-Tesla people that use the chargers via a 3rd party app or something should be aware of this unusual but not unique situation.
In my opinion further description isn't necessary, but if you've visited the place before and feel the need to add more info - please go ahead, you're most welcome to do so. I might be able to add some photos from my time lapse recording on Google, in order to guide people visually through that maze. It's huge, but so is the shopping mall above.

As you've found out recently, the current opening times of the *parking garage* are displayed on the Tesla website referenced in the node. These are subject to change without notice. This is also displayed when navigating there; the car will tell if this charger can be used according to the ETA of the route.
Judging from other SuC with restricted opening times, I would say this supercharger does operate 24/7 IF you're in there - but entering before 6am or leaving after midnight might be very troublesome.
Walking to the ticket machine (and back) for after-hours parking isn't necessary, it's on the route to the exit.

Come again? No free map service provider has current photos of this location yet, but there's a) Tesla stating that there are additional Tesla Supercharger stalls since about June, and b) there's this https://maps.app.goo.gl/e71ao1h9bvDR2w4v7 photo (and a couple more) that verifies the second row of parking space has indeed been converted to fit a partial row of V4 stalls. I don't see *ANY* problem with adding this information before new satellite imagery goes live, especially since the current rectangle doesn't fit sat data of the actual size of the supercharger location. Do I have to travel there myself and get an additional photo of the location, is that an "authorized" source for an edit?

Check https://www.tesla.com/fr_LU/findus/location/supercharger/portesdangerssupercharger.
Google Maps also has a photo of a new row of 6 V4 stalls in addition to 6 V3 - from a layout perspective, that doesn't make sense, this is likely 8xV4 plus the existing 12xV3