First off, change over to SMB from AFP. SMB has been the default
network transfer protocol since Mavericks. You should see a performance
boost in network transfers.
As far as upgrading, do a little home work first. Check to make sure
any of the apps you use are compatible with High Sierra and if it may be
necessary to upgrade (meaning pay) to be compatible. You should also
do so with any third party hardware devices that you have.
Make sure at a very minimum (though it looks like you may already have)
to back up all data as anything could possibly go wrong with the upgrade
that have nothing to do with the upgrade itself.
In addition, though not necessary, it may be a good time to do some
housecleaning on your Mac like getting rid of apps you never use, archiving
data that you don't access everyday to external storage, etc.
As I started, switch over to SMB before anything.