Different room for dancing

I think how well this will work has a lot to do with your guest list. If that 300 is almost entirely younger people, then going up and down stairs (even if there is an elevator) for the dancing/party portion of the evening might work out great. However, if your guest list is diverse, e.g., there will be a lot of older people, a lot of extended family, and a lot of younger guests, I could easily see it ending up like there are two different parties going on. If you spend a significant amount of your time/energy at one of those two parties than the other, the guests at the part of the party you're not at much might be pretty offended. The rooftop/ 3rd floor dancing space seems like it would be a better option for a late-night after party. If the second floor space can seat 400, why can't they incorporate a dance floor along with your 300 guests? It seems like 25% of the space should be available? If you're the poster I'm thinking of, in other posts you've mentioned your large Sicilian family. That makes me think there will potentially be a lot of older relatives, and you mentioned your mom is pretty opinionated, if that's all true, I'd think the split-level reception is just inviting complaints and trouble.... Good luck!

We looked at a few venues where the dancing was on a different floor and ultimately decided against it as we felt it chop up the party too much (think first dances, father-daughter dances) and that people who did not go up to the dancing room would end up leaving early.

The other thing we considered were the older guests, who would probably like watching the dancing but not actually participate