I am not saying that you have to build the site in .NET Framework. You can pick any technology which you like. I specified it just as an example. Before you hire a developer and pay him, you should write down couple of points such as
1) What does the web application do
2) What are the core min features that you need to satisfy first few users (don't get into the habbit of feature creep)
3) What is your intended audience
4) What is the core problem you are trying to solve.
Also as a prototype do you really need the Database and other stuff. It should not matter what database or language or framework you use but you should be able to answer the above questions.
Don't listen to the people who say one language is greater than other language. It shouldn't matter. You should pick one which is easier for you and others who join you later.