Lost on NewEgg: Best Router to do this...

An internet-less wireless local network:

I'm looking to build a simple wireless local network comprised of the following:
1. A wireless N router or access point
2. One or more PCs wired to the router that will act as NAS
3. A tablet that will allow me to access and work with the files anywhere in the office. [I have a nice 64G Toshiba already]

Wired/Wireless security are key here. I do not want the router or any wired PC to be connected to the internet. No Internet Access via this router! Can a router work like this without being connected to the internet?

the wireless router should only allow specific devices to connect to it (i.e. only my tablet)
Can I specify on router settings what Mac Addresses are allowed to connect?

I want a fast connection so I do not necessarily want to encrypt all wireless traffic.

Any ideas on an Android App that will best enable me to access shared files on a local network?

Thanks for sharing your expertise!