Xbee module and Gateway Selection

We are planning to use around 200-250 nos of wireless ZigBee modules in one of our projects. Based on our requirement, it will be a Single Point to Multi Point Bidirectional Model, where a ZigBee Gateway acts as Single Point (Master) and 250 ZigBee modules will be acting as Multi Point devices (Slaves).
The ZigBee Gateway has to communicate with SCADA software running on a PC and should be able to Transmit and Receive messages from all the 250 ZigBee Slave modules.
Each ZigBee module should be interfaced with a PIC microcontroller through SPI/UART.
There will be no communication among the modules. All the modules will communicate only to the Gateway.

We need assistance in choosing the Gateway and selecting the right module among Xbee3 Zigbee, DigiMesh and 802.15.4 modules.

What would be communication protocol between the Xbee GateWay and PC?
Whether a single gateway be able to communication bi directionally to all 250 Xbee modules?
Whether any repeaters or signal boosters need to be planned, considering 70 meters of indoor coverage?
Whether any RF signal interference will occur if all the 250 modules are placed in a same room?

Thank You for your time!

Please contact Digi Sales at sales.questions@digi.com so they can help you determine which products to use.