You should be able to buy 2 x EX4300-48-EFL from your local Juniper reseller and generate a license to support VRRP.
The reseller doesn't need to know the serial number as you are getting an auth code which you combine with the serial number to generate the license.
In general licenses are not enforced but generates a warning if you configure a feature which requires a license. But it still requires you to buy the license to be in compliance with the software agreement.
More about licensing here: https://www.juniper.net/documentation/en_US/junos/topics/concept/ex-series-software-licenses-overview.html
You can buy a 4 x SFP+ uplink module for the EX4300 or if you just need virtual chassis, use two of the four 40G ports on the back. You just need to ensure that they are configured as "vc-ports" to use them for virtual chassis. You can find cheap 0,5-1 meter QSFP DAC cables for virtual chassis.
Virtual chassis doesn't require any license except on the EX2300 series.
If you don't have any specific requirements in regards to features I would recommend you to use the JTAC recommended software release for most stable operation. JTAC recommended software releases can be found here: https://kb.juniper.net/InfoCenter/index?page=content&id=KB21476