I have an HP T740 running Opnsense and it works just fine. You can pick them up for about $100 USD, and they seem to come mostly with 8GB RAM, and a 64GB SSD. That seems to be more than enough for Opnsense, even running VPN’s.
These are just a tad larger than my Lenovo M910Q Tiny servers, but they have a PCI slot, so you can put a second ethernet port (or 2, or 4) of whatever speed you like in it.
The question implies that the OP wants to create one giant filesystem with all of their data on it. This has its own issues, especially if it is in /home. For one, as someone else pointed out, it’s fairly difficult to run your system without /home mounted, and that makes it difficult to resize. Sure, you can set up an admin account with it’s home in the /root filesystem and then log into that - but that seems to be a lot of work in itself.
If it was me, I’d set up mount points for file systems that make sense. Maybe /data/Photos, or /data/Music, or data/AppData, or whatever. As much as possible, I’d just point whatever software I was using to those new directories to find the data. If that isn’t feasible, for whatever reason, then a symbolic link from /home/Photos to /data/Photos will work seamlessly in most cases.
As far as I’m concerned, after administering enterprise systems using Unix going as far back as the early 90’s, symbolic links are a key tool in managing disk space that you shouldn’t just dismiss because it’s “an unnecessary layer of complexity”. Having smaller, purpose designed, file systems allows you to manage them better. Sticking everything into /home is probably not the right answer for anyone.
Resizing partitons is often not necessary. Use a symbolic link to relocate a subdirectory to another file system. For 99% of use cases this is indistinguishable from expanding the partition.
As an example, I was setting up SnapCast on a Debian LXC. It is supposed to stream whatever goes into a named pipe in the /tmp directory. However, recent versions of Debian do NOT allow other processes to write to named pipes in /tmp.
It took just a little searching to find this out after quite a bit of fussing about changing permissions and sudoing to try to funnel random noise into this named pipe. After that, a bit of time to find the config files and change it to someplace that would work.
Setting up the RPi clients with a PirateAudio DAC and SnapCast client also took some fiddling. Once I had it figured out on the first one, I could use the history stack to follow the same steps on the second and third clients. None of this stuff was documented anywhere, even though I would think that a top use of an RPi Zero with that DAC would be for SnapCast.
The point is that it seems like every single service has these little undocumented quirks that you just have to figure out for yourself. I have 35 years of experience as an “IT Guy”, although mostly as a programmer. But I remember working HP-UX 9.0 systems, so I’ve been doing this for a while.
I really don’t know how people without a similar level of experience can even begin to cope.