Please correct me if I'm wrong, but I understood that you're using a multi-user system. The script currently will mount the network share under the same user, urs. I thought I should mention in case you prefer to have the same behavior for any other user to use the variables, in order to make it more flexible (i.e.: $SUDO_USER instead of hard-coding urs, etc.).
I'm not all that experienced to be honest... but I'll try answer some of your questions 
The built-in file manager that comes with the Gnome desktop environment, Nautilus, has its own implementation of various network protocols (GVfs — GNOME Virtual file system). That's why you can use it without any additional dependencies to connect to the network drive or server.
However, those dependencies are not transferable, if you will, to the rest of the system. That's why you need to install additional packages, cifs-utils in this case, to instruct to perform actions that aren't specific to any of the GNOME applications. From there, it's a matter of understanding what this package provides and how it works. As per the documentation:
File And Directory Ownership And Permissions
The core CIFS protocol does not provide unix ownership information or mode for files and directories. Because of this, files and directories will generally appear to be owned by whatever values the uid= or gid= options are set, and will have permissions set to the default file_mode and dir_mode for the mount.
In regards to if and when will GVfs make any updates (I'm also addressing point #2): I have no idea. You may ask in the Gnome forums about this.
Please also note that Zorin OS 17 uses Gnome at version 43, whereas the latest at the moment is 47, which has significant changes. Some of them are in the network department, but I'm not sure if they are quality of life or something behind the scenes.
I couldn't find any official help page on this regard, but it's not too difficult. Zorin OS ships with UFW — Uncomplicated Firewall. You will find it listed in the applications menu as "Firewall Configuration". Enabling it's just a click away, and setting up rules is quite straight forward using the graphical interface, at least for the most common use cases.
The help page regarding anti-virus are very short: Is an Antivirus Necessary? - Zorin Help. This has been discussed many times before, and everyone has a somewhat different take on this.
In my opinion, the best anti-virus is your common sense: don't download random files from the internet and avoid installing software from untrusted sources. What a "virus" is has changed a lot in the last decade. What used to pass for a virus 10 years ago is today considered an essential feature...
Here are a few threads to go over some more opinions:
I have no idea about this. I'm sure there must be a way, but I'd recommend starting a new thread for this, to keep things organize and address one issue at the time. This makes it easier to later search for specific issues, including those making online searches that are lead here.
By the way, just to be clear since you are asking about "official recommendations", these are my own opinions and not necessarily the official stance of the Zorin OS developers.