In terms of stocking string, I keep a reel each of a good syn.gut, a good multi, and a good poly (I don't do cheap restrings!) and if a customer wants anything specific i'll order it in (usually next day if I order before 3pm). This means my outlay is lower initially and I cover most bases for the average club player but can offer everything else for people who want it.
You've made a decent start - just a few tweaks and you'll be good to go!
I tweet - @ashtennis guru (no spaces)
I Shoot - www.flickr.com/photos/ashtennis guru/ (again no spaces! grrr)