Theres so much to unpack...! But ill try and throw something in the mix.
I dont know if freenas/ truenas supports a lot of addons or whatever they call it but the moment you mentioned media and games my thought went to proxmox, though i suppose you might also be able to get away with a bunch of docker containers.
Soo.. proxmox (or any hypervisor) will allow you to run multiple segregated VMs and containers.
On one vm you can install freenas/ truenas (whichever the good one is atm, im a little out of touch) and allocate the bulk storage drives to it.
Another vm for Plex/jellyfin
Another for minecraft, factorio, tf2
Another for nextcloud/ webserver
Nextcloud provides webdav/ caldav for calendar and contact syncing so sorted there. It also has a collabora app i think for collaborative document working.
In terms of security, you want to follow nextclouds secure configuration guide as a start.
The best way is to use a vpn to access your home network. Maybe give the others access if you trust them but you may then need to do some vlanning and segregation to protect the rest of your home network from them.
If you must expose to the net (which you may do with the games servers) then again, the config guide has you covered, use crowdsec, use https, use random ports, use strong passwords and mfa.
Do regular backups. 3 copies, 2 separate storage mediums, 1 offsite (3-2-1 rule).
Idk about the 8tb drive.
The above isnt the be all end all. Let it be the start of a discussion and your research journey