Good luck Andy, a righteous but financially challenging endeavour!
I have been growing and selling pretty much full time, for the last 3 years based on Charles’s methods, and probably have a mine of information that would probably be very useful to you, but no time (as i’m a grower), time is a precious commodity) to tell the story here 
Suffice to say , salad leaves are the only crop that will make you money, and ‘subsidises’ the veg, which are important, positive and beautiful to grow but , i’m afraid to say pretty much unviable from a business point of view.
Salad leaves and the supplying thereof is a complex, complete art and a deep subject!
I would recommend Charles’s market growing course, a no brainer really as he is doing them at the moment.
Also have a look at this article :
I would to like help you, but so limited on time, but here is my email anyway,
hazelrowanwood (at) gmail (dot) com
good luck indeed!
Dan