WSN (XBee)temperature and humidity

Dear forum member,
I want to build my ZigBee networks containing 5 XBee Pro S2(5 Arduino Uno) as Router and one gateway CPX4 as Coordinator.


—>In the gateway:

*PAN ID: 0x4a59
*channel: 0xc
*scan all channels

---->In router XBee Pro 2:

*PAN ID: 4a59
*channel scan: 16
*DH, DL destination: 0

I choose the star topology because each xbee module will send a temperature and humidity value to the server through the gateway.
These XBee modules receive nothing from gateway.(modules---->gateway).

It’s the best choice or not ?if you can give me suggesions?

How packets flow in the network to zigbee?

A single packet of the last xbee contains all data from the other xbee ?
or each xbee is send a packet to the gateway ?!!

I can implemented the protocol CSMA / CD (Carrier Sense Multiple Access / Collision Detection): the module xbee sent these doonnes when the channel is available??!