Really depends on what you want to do.
Atm I'd only buy a cheap starter ship (there area few) then work in-game to earn credits and try out different ships, or when CIG has a "free fly week" when you can try different ships for free (they happen a few times a year).
Once you know which parts of the game you like the most (be it mining or bounty hunting or whatever, then if you want buy a specific ship.
IF things will work out like CIG has said they will, then we as and org will be able to pool ships too and allow different members access to some of the ships placed in the orgs storage, so you might not need to buy anything bigger at all.
But atm id buy a starter ship just to get going.