Good afternoon,
Likly you have an idea of where your router is going to be placed... Maybe in a designated rack/room/table etc. Well that location may not be best suited for the job or for RF... IE if your 'computer room' is in one corner of the building and your users are in the opposite corner, you may not have the best coverage or any coverage at all... You will then end up either buying another AP or running a series of network cables to your router.
Likly your best bet is to go with 2 devices as to be more flexable.
