a couple of thoughts to add. 80% of the volume and sales happens in 20% of the time. When is the busy time and what is the busy day(S) watch then…you will get a feel for the passing trade and traffic and custom base, you can extrapolate the rest, an average spend can be estimated in a range.
Costs wise …weigh your ingredients and add a cost per kilo you can work our the cost and sale and margin and helps you manage your costs (dont overadd the expensive ingredients, but also aim ofr consistency…notice the way sub way manages their portion control.) Hope this helps