The PIC18F4620 should have all the goodies you need to setup you network if I understand what you at trying to do.
I would caution you to spend the time it takes to understand section 17 in the datasheet.
For this PIC the I2C address is set in SSPADD.
I2C can be setup as multi master.
I2C Bus: Multi-Master .
The section in red is good new. Each PIC on the I2C bus will know when the bus is busy. In reg SSPCON1 there is even a bit to determine collision: WCOL: Write Collision Detect bit.