I think it's a great idea. It's something I'd enjoy doing. Are you familiar with Eliot Coleman? He grows vegetables year round for restaurants. I'm sure it could be applied to herbs. I'll include a link below.

http://fourseasonfarm.com/main/articles/articles/mother2.html Another article I'm sure you can gather info from.

Year round will depend on what you work out with the restaurant(s). I wouldn't hesitate to talk with them about spring to fall crops. Find out what the prospective buyers want and see what you can do. If you find it works for you and them and that you enjoy doing this you can add to your operation later. We're adding a tunnel in the spring. This winter I'll be growing in cold frames in our greenhouse. Smaller steps at a time is usually a lot safer than diving in head first. Good luck!

Here is a link that might be useful: Winter Harvest