Separate VMs in separate VLANs for private and shared storage. Makes things a bit less convenient for you, but worth it imo.
Somewhere between $1000-$2000 I imagine.
RAID is great for minimizing downtime but is never a replacement for a backup. The 3-2-1 rule mentioned below is a good thing to follow.
Never grant higher permissions than necessary, never open more ports than necessary. If your gaming server VMs have no need to communicate with your Nextcloud servers then setup deny rules in your router firewall to stop that traffic from being possible and so on.
Get a proper physical firewall device that allows you full control. I usually use opnsense or pfsense as the software OS.
Both DS220+ and DS224+ has been a pleasure to setup, but I wouldn't replace your DS218+ just because. Just make sure your RAID is healthy and your backup too.
An alternative to a standalone NAS is to setup your own little ITX server. Only if you enjoy tinkering though, Synology is definitely easier.
At home I'm currently running Server/NAS/Gaming PC all in one.
It's a Debian 12 KVM/QEMU host with an m.2 NVME disk for host OS + VM OS and 2x16TB Seagate Exos disks in RAID1 for data storage. The other hardware is a B650 ITX Motherboard, AMD Ryzen 7600 CPU, 2x32GB DDR5 RAM and AMD Radeon 6650 XT, Seasonic FOCUS PX 750W PSU.
With my KVM/QEMU host, Game Server and Jellyfin Server online it eats about 60W-65W, so not that bad.
The GPU and an USB Controller is passed through with VFIO to a virtual Fedora that I use as a desktop and gaming client.
Just make sure to have a sound dampening pc case so you can keep the servers online without being bothered. The GPU goes silent when the gaming VM is off.
I've never tried to run multiseat the way you do here.
I do however succesfully run multiple computers in one chassi using kvm/qemu with pci-e physical passthrough on gpu and usb controller to my virtual fedora gaming machine (using vfio drivers in the host). Definitely more overhead than multiseat but I do enjoy the easy backup and restore I have on my gaming machine.
If privacy is of utmost concern, we recommend that you refrain from communicating any personal data to us since plain-text email is not a safe media for communication. If necessary, use PGP-encrypted email.
...
...
We do use a third party to operate our email service, so we remind you to carefully read #1 again.
In some circumstances, pages may need to be protected from modification by certain groups of editors. Pages are protected when a specific damaging event has been identified that cannot be prevented through other means such as a block.
When I switched from Windows to Linux I found cockpit-project.org to be a true blessing when troubleshooting. Something about having logs and services in a Web GUI that can be really helpful.
Login to your router or wireless access point and check what devices are connected. Then setup mac adress filtering to improve your security, if you can be bothered to have to add your devices mac adresses manually.
mac adresses are easily spoofed though, so it isn't foolproof.
I still run everything I can as .rpm through dnf on my Fedora and .deb through apt on my Debian servers.
I only install a flatpak as last resort.
From a dev viewpoint I can understand the gains of flatpak but from a user viewpoint I prefer a "real" install.
If you're already into self hosting, programming, networking and automation then I don't think you'll have any trouble.
With that background you should be able to google the solutions.
