Of all the information you shared, the one thing that jumps out at me first is the parking. You need to check your local parking codes. If I remember right, there is typically a requirement to provide one parking space for every so many people. In my case, the small town was satisfied with the available on-street parking and the small municipal lot in the rear of the building, because it was a downtown location. But, I believe some cities will require one space for every 3.5 people or something similar. If that were the case, your parking would only be enough for about 227 people including both the theater and restaurant. You have to assume that every seat is filled; so, you can't create capacity greater than your parking will allow for. One helpful thing is that often cities do not apply the parking rules in downtown areas. You just have to check and see what the parking code is for your site.
As for the poor condition of the property and needed upgrades and renovation, I can sympathize. I went through something similar. It is always hard to estimate the cost of that kind of project. Whatever you think it will be... double it and maybe you will be close.
If you provide public access to the balcony, either as a balcony or as a second screen, you may need to provide handicap access as mandated by the ADA. Since you will be doing major renovations, handicap accessibility will be required in most of your facility with only a few exceptions (maintenance spaces, etc). In some locales, officials may even want you to provide handicap access to the booth. For sure, any stage or performance areas have to be handicap accessible. Check out ADA requirements before you go too far. It can be a deal breaker.
If anyone is interested in a theater that has already been twinned and renovated, I have one for sale in Oklahoma. No construction headaches, just a turn-key operation. A buyer could have it going again in short order.