One step with a 400 pound electric wheelchair is a mountain.
The bathroom on the first floor will work fine. Anyone in line will let a wheelchair go first. It's spacious inside but don't go on the weekends at night, it won't be comfortable due to the crowd size.
One of the security guards can probably help you up the one step by their entrance. There is a unisex restroom on the first floor that you should be able to get into with a wheelchair. I hope this helps you out.
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