Lets say on my host I run nothing other than a firewall plus a Virtualbox and KVM each with a unique Whonix installed for diffident online activity.
I have set up my GUFW today to block outgoing and incoming traffic, apart from ports 80, 443, 53 which are still outgoing, previously I was only blocking incoming traffic.
Whonix booted up fine and is running ok at least to browse, so I just want to make sure that I’m not blocking any important ports that Whonix needs open to function correctly?
If the purpose is to block leaky apps on the host then its a very poor way to do so. Almost any traffic will use these ports. Your best bet is something like Corridor which would block any non Tor traffic coming from misconfigured applications.
Another problem with this is Whonix is likely not going to be ale to connect to Tor by default because most guard nodes use ports different ports than 80 and 443. Unless you add the facist firewall setting to torrc. Downside is you are chosing from a smaller subset of guards which can increase chances of picking a malicious relay.
PS
On GNU Linux (except on Ubuntu or if you install proprietary software) apps phoning home behind your back is not a problem you should worry about. Limit your activities to Whonix vms.