Start with something small and you can always upgrade your hosting plan to grow with your business.

I doubt your hard disk is going to be the limiting factor; disk space is so cheap as to be not really worth worrying about. Instead, worry about your memory, processor speed, database optimisation and ethernet connection.

Anyway, as Danu says, start small - why not just build the thing first and see how it goes?

yeab Space and Bandwidth are probably the biggies as a dating site will probably have to hold loads of pictures