A protien skimmer, with live rock and supplimental circulation, can replace a normal filter. If you're not getting live rock right away, you do want a more traditional filter for the bacterial colonization space.
For a fish only tank, you don't really need the skimmer. Sorry, I forgot to account that you were not getting your live rock at first.
Sounds like you have a decent LFS
! They actually told you not to buy something! (Or were they trying to sell you a more expensive product in it's stead?)