Frac T1 Connectivity

Simple scenario:
i need to hook up 4 channels to local network.
I was told to use cisco router ( 1720 ? )
and adtran CSU/DSU ( phone system in place )
Since i have no experience with Cisco Do you have suggestion what IOS i should use if i am going to use NAT on that network. Should i use firewall IOS? Also what feature cards and cables do i need. – I am trying to find a source where it is all expalained but no luck.