I know I drone on about these sorts of things, and I do apologize up front. Lunch is VERY, VERY lucrative for some of the people I have talked with. Some it is a pain in the neck with little return.
It sounds like you need one of them “business plans” I’ve heard talked about. Really, the decisions you are asking us about, we can give input for . . . but only you will know you area, market and what you want to do with the business. Develop a written business plan that identifies the target market and what they potential products are to sell to the identified target. you will likely need to research what is and is not selling in your area, what the financial info is for your people, and the like. Once you have written out a description of what your business will look like, the questions like this are easier to filter through.
In general, I (in my limited experience) recommend a varied menu in order to attract more interest and more repeat business (and offer more up-sell opportunities). The fewer people in your target market . . . the more variation might be needed. Our pizzeria has LOTS of item types for our 3000 or so people in our delivery area. We started marketing county-wide to build more traffic. The variation is attractive to people traveling 20 minutes with a family with varied tastes. OOOPS! There I go assuming. Are you looking at delivery, carry-out, dine in? Menu and styles of food can vary on business model.
All the answers will flow/filter through your business plan.