You won't be able to get 350 people and a stage/catwalk on one floor. I recommend finding another location.
I had my wedding there and we had about 110 - 120 people, and it was really tight. There is also only one changing area that's technically a conference room on the floor below. It's a beautiful space but this is not the venue for your needs. If you like the industrial look, there are some really cool spaces not too far from here.
They have different floors and levels however with the block tower events it only holds 40 people I think at the top level. I know they do a lot of shows there however so you might be able to just might go through a different company.
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