For example, general advice is to have the related/established firewall rule at the very top.

In my case however, I have 20+ firewall rules before that, but all of them are disabled.

Are disabled rules evaluated? Do disabled rules affect performance?

In principle disabled rules are not evaluated, so they should not affect functionality or performance.

It is a good practice to entirely remove disabled rules if their usage is not planned anymore ... disabled rules make readability of setup much worse since property "disabled=yes" is not highlited and it's easy to overlook.

For maximum performance limit rules above the established/related rule to those rules intended to break established connections for some reason.