Bonjour Joanna, and welcome to the site,
Just a thought, but instead of looking to develop a marketplace within France, why not take advantage of your location to sell French items to the rest of the world.
I'm no expert in Traditional French anything really, but I'm sure there has to be jewellery, craft, collectables, ect, all unique to France or local areas throughout , and those types of products could be a gold mine for those with a love of the country, but living 20,000 miles away and no access to them.
Just a thought, but it's what I would be looking at doing most certainly.
Good luck with it!