if ur gonna get 40k may i suggest that u get a common army like Space Marines or Elder ( even though i think SM suck )
once u get a hang of the rules you can move on to different armys i.e Tau ( best Army of em all ) an so on
One thing you absolutly must understand first - this game will consume your soul if you let it. Secondly, it will also consume your wallet. Other than that it is the most fun, non-electronic game (both fanstasy and 40k) that I have ever played. I say go for it.
If you love tabletop gaming, and there are people around you to play with go for it. I have an army and theres only like, 3 other players in my city. I still think it was worth it to have my army sitting on a shelf looking awsome as hell. I use Tau myself. I'd suggest searching a file sharing netowork for all the army codex books first and decide what you want to play that way. And as far as buying an army for someone second hand, that would be alot less money most likely, but youd either have to stick with how they are painted now, risk damaging the pieces when your striping the pait, or try and paint over whats there.