I was faced with exactly the same a few years ago after buying a set of foam cored wings NIB. What resulted was something that fit my love of the earlier eras of flight. It started with a simply rough sketch of an open cockpit design and ended very well with a plane that looks good to me and flies very good.
The first step was similar to what you are doing, establishing some good numbers to work with. If you are an experienced builder... they are all you need. The shape and design simply needs to conform to those good numbers.
You may enjoy a look at that build log.
Big Red