A long sleeve shirt will be fine
If you are not really a tie person...you really don't need one. But a nice jacket and slacks or a nice black or muted blue jean's with tasteful shirt and jacket will work. Or even just a nice long sleeve dress shirt without the jacket and quality/comfortable pants would suffice.
Biz casual seems appropriate
Business casual will also be nice.
I would recommend it. It's a fancy restaurant.
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