Multiple WiFi Access Points in Big Concrete Building

I'm looking to install WiFi coverage in our big concrete building. I recently purchased an ASUS RT-N56U from Newegg for my general area of the building. However, I'm looking to setup a professional type wireless network in and around my building with multiple points of access (I most likely need like 4 more Access Points for WiFi). We have an existing wired networking in the building.

I have a few questions...

• Can I just buy 4/5 wireless access points that go with that router? Like these: ASUS EA-N66 & ASUS USB-N66? They should work with the router, right?
• Can they all share the same SSID & Channel or do I have to run them on different channels?

Depends on the size and just how professional you want to make the network

You can setup a little network using lots of WiFi routers, but if you are using individual systems like the ASUS's you linked to, any password changes would have to be done on each router.

You can use the same SSID & password to make a continuous network, but if the signals of one router overlap with another you will have to change the channels so there is no interference, something quite easy on a 5Ghz network, but harder on a 2.4Ghz.

Understanding Wi-Fi's two spectrum bands

Alternatives would be using systems like Meraki however they are a lot more expensive but management is made a lot easier.