There's several movie houses here in seattle that have other stuff like coffee that could be sold to non-movie patrons. Is that what you're talking about? Or are you thinking about the movies going on in the background of the coffee house?
Profit margins I think largely depend on your ability to manage your finances. You might consider picking up a few books on starting a coffee house as a way to get your preliminary numbers. It's a pretty big undertaking and I can't tell you enough the benefits of planning your venture well. What are you going to serve? Who are your vendors? How are you going to get your movies? Etc.
Chris.....You might want to contact "Lumiere Espresso" in Monterey, CA. They're essentially what you've described. But I'd humbly recommend investing in a mobile coffee/bakery/chocolate cart or kiosk as your operating base. If you can hook up to their water, electric and drains, that's great, but I'd be very conservative in building upgrades. (you may have already thought this through, no?)
I'd be very surprised if anyone would openly share their gross/net information, and frankly, most business plans I've been privy to work with reasonable projections based on projected foot traffic. Based on my preceiption of your comments, the movie theatre may be a very far second issue to the accessibility of the coffee operation to the general public. Lumiere, from my observations, appears more like a coffee location that "happens" to be located in the outer edge of a theatre venue.
Not knowing your business background, so much of this may be obvious, but certainly would come up in open discussions with any business group. I'd recommend talking to small business owners near this proposed venue and ask open ended questions about how they see foot traffic, what patterns they've noticed, the level of optimism for other retailers in the area; expansion, cutting back, etc. They live their business life in the area and will probably have valuable input.
Another incredibly important issue relating to your ongoing marketing of the project is signage and what your city will allow. You'll possibly be hidden inside of another, more visible retail venue, a theatre. Unless you're sharing whatever square footage of signage is allowed by the city, you may be relying on secondary benefit of a sign that touts "theatre." Now you have to build a clientel without the benefit of "drive-bys." Basically, I see the theatre as less important than just positioning the coffee operation in that business district. Just some thoughts.......... have you thought about asking Matt right here on the BX site? Both his school and other consultants on the internet do present "sample figures."