Installation of Free with opting in to Premium on 60-day trial

I today installed Avast Free Anti-Virus software. During the installation Avast offered me to upgrade to Premium for 60-days free, with a multi-computer annual subscription fee of roughly $80 assessed if I do not cancel within the 60-day period, which I accepted. How many computers and cell phones are allowed to be part of this plan?
How do I know what the precise version of my Avast software is, since you have many paid subsciption offerings available?
I now want to install this same subscription on my 3 other computers and 2 mobile phones. How do I do this without Avast setting each one up in a different account?

As an Avast Free used I don’t know that, but I certainly wouldn’t have signed up until I knew.

I would also have tried the Avast Premium product before making an informed decision.

See https://www.avast.com/en-gb/premium-security#pc and https://support.avast.com/en-gb/article/activate-premium-security-multi-device/#pc
Hopefully they will help.