You can find a detailed list of questions that will need answering in your retail business plan on the Uncle Max Says website.
There's also a very useful article on retail business plans from the Canada Business site for entrepreneurs.
Two books worth checking out are:
Smart Retail: How to Turn Your Store into a Sales Phenomenon by Richard Hammond
So You Want to Own the Store: Secrets to Running a Successful Retail Operation by Mort Brown
If you have come across any other useful resources for developing retail businesses, such as books or websites, please let me know by emailing resources@ business-plans.co.uk.