arduino and xbee in mesh network

I'm working on aproject with xbee(s2) and Arduino UNO , My plan is to create a mesh sensor network from 5 nodes , each node consist of xbee connect to Arduino through xbee shield, and number of sensors connect to Arduino , one of this node must be as xbee coordinator and the others as router or end device . My question is in which mode must I use in each xbee (AT or API mode) and why??? And can I use the coordinator as API and router as AT mode or I must use all of its node in API mode to verify mesh network and why?? Please if any one Know any idea about it or any useful tutorial on how to set up arduino and xbee to recived sensor data packets from each node