Facebook was built with experienced people over quite some time. I would recommend you start with smaller projects that are useful to YOU.
I have met many prospects who had the next Facebook in mind, and I've turned them all down because it simply doesn't make sense. Even Google can't fight the popularity of Facebook, and very few competitors can monetize a social network.
I suggest you take some time to learn HTML and CSS
correctly, then start working with PHP and progressively move on to bigger projects.
If you still wish to pursue your project, then look into hiring a freelance web developer and pay him weekly. I don't know any dev worth his salt that would work on the promise of future profit.
If you're looking for a reliable host, A Small Orange has fantastic support. Once your site grows, you can always move it to Linode or some other VPS. The most recommended hosts are always A Small Orange, HostGator and Linode, in order of power requirements.
PS: Start small before you dream big. Good luck!
