Developing a magento module for marketplace / multi vendor

Question

I need a module that serves as a marketplace / multi vendor system for Magento. I searched on the web to see if I could buy one, and found some. One that got my interest was: http://store.webkul.com/Magento-Extensions/Magento-Marketplace.html

But the problem with all of them was, they keep a unified catalog.

In my case, imagine that I would like to create a e-Commerce where there are a lot of pizza places, each pizza place with its own menu. With a unified catalog, the user would enter on the website, see all the pizzas, and when choosing from a pizza nearby, they may not have the kind that the user wanted.

So that's why I wanted a module that first: 1. Show the places nearby;

1. Then, with a specific place selected, show the catalog just for that place.

2. At first, when searching for products on the website, show the product and who is selling it, instead of just showing the product, as it is right now with this module mentioned above.

I thought of buying that module and write code to fit to my needs: 1. Associating the product with the vendor who added it, and when showing the catalog for a vendor, show just the products that he added;

1. Override the catalog search module. Showing instead of all products, show the nearby vendors and a small list of their products;

   but since I don't have access to the code of the module before buying, it may not be a good idea.... who can ensure that I will be able to perform those modifications?

So, short: What is a best approach to develop such a module in Magento? Thank you.