You need to re-source ~/.bashrc or open a new terminal to apply the changes.
This is correct:
alias foo="sudo reboot"
It means make foo an alias of sudo reboot.
This is wrong:
alias foo=sudo reboot
It means make foo an alias of sudo, and print the value of the alias reboot.
Yes. upgrade is the actual command, but update is an alias of it (this is a dnf internal alias, not a bash alias).
dnf automatically refreshes the cache on a timer, and also when it’s used if the cache is stale. So there is no need to update the cache manually like apt update.
For more information on common apt vs dnf commands, see: