Cisco Callmanager - Remote site, how many phone lines and what type?

I have a remote site that I am going to add to our Cisco Callmanager VOIP phone system.  There are 7 users right now and that could grow to about 12 in the next year or two.  I have a 2811 already out there that I am going to use.  I am strugging with how many phone lines I should use for this site... They are going to use local lines for incoming and outgoing calls, just not interoffice calls.  My plan right now is to just start out with 4 POTS lines, but is that a mistake?  Is there anything else cost effective that might scale a bit better?  Also, is 4 lines even enough?