Hello,
QFX5200, EX3400, EX3300, EX2300, and EX2200 switches cannot be part of any mixed Virtual Chassis. Multigigabit EX2300 switches can form a Virtual Chassis composed of only EX2300 multigigabit switches, and cannot be mixed with other EX2300 switches in a Virtual Chassis.
If you want to have one virtual chassis between two EX2300 & other virtual chassis between EX3400, then that is possible.
On ES2300, you can not use RJ45 ports as VC port.
Regards,
Rushi