How many equipments can be connected to the eWON on Modbus RTU

Standardly every "RS485 driver" can drive 32 Slave equipments.

But if the Modbus Slave equipments have an high input impedance, then you can drive up to 255 equipments.  
For example, if your slave equipments are built on the same RS-485 chip than the eWON, then you can build a network with up to 255 equipments.
Pay attention that the network must be terminated and polarised to achieve such performance.