Generally you would need to research more on the product and most likely not need a patent for a product that has an existing patent. I suggest you understand the Spanish product and EU patent laws before you make a decision.

If you have not tried buddypress have a look at it and see if it can do for you what you are looking for.

Your idea is not new, however it is a great idea that requires more than just being an idea. What you need is a lot of determination, planning and funding to get started. It is an idea that lacks detailed reasons why your new e-store should become a success after entering a market that is already flooded with similar businesses. To decide the final part of your question you need to ask yourself why you want to do that kind of business, how much you are prepared to invest in the idea.