Looks like you already settled on this, but I’m doing exactly this (syncing obsidian, as well as photos/videos from camera reel), to desktop and NAS, using syncthing-fork. Let me know if you want some pointers.

CPU and RAM are not the only limiting factors. Not only that but not everything runs multithreaded. Maybe some piece of the puzzle is not multithreaded and is using all it can from a single core (assuming that cpu is multi- core)

Depending on how much you value your time, you’re almost certainly better off getting a new machine to run pfsense.

I have found synching to be very useful for making copies of files across devices. I have it setup to mirror photos from my phone, photos from my wife’s phone, and various other things (to-do lists for todo.txt, notes and shopping lists for obsidian… stuff like that) back to my desktop and my NAS. You can set it to do one-way sync (which is more like a backup) or two way sync (where changes anywhere are propagated to everywhere else).

As others have said, it’s not really a true backup solution, but handy to have immediately accessible copies of what’s on your phone in case of phone loss or damage.

For photo viewing and sharing, I am more or less pointing the photo sharing app on my NAS to the photos I sync from phone. They all get dropped into an “inbox” when first synced and then can be organized from there.

You may also want an actual backup solution. There are quite a few and that’s a different topic. The reason I bring it up, though, is that simply mirroring what’s currently on device is not considered a real backup by most people, and for good reason.

Oisd.nl

Depending on how in depth you want your firewall, packet inspection, etc to be and your internet access speed, you may want a commercial grade router. You can also probably use an old PC and add a dual gigabit NIC to it and load up opnsense or pfsense or some other router/firewall distribution. From there, add a stand alone switch and a standalone wifi AP (or router in AP mode). The reason I bring up using a commercial device or an older desktop is because packet inspection, filtering, etc at line speed on a gigabit connection won’t be possible with a lot of low powered devices.

I used to do this (was using an old Intel core i5 second gen with added RAM and a dual port gigabit NIC) but it was a lot to keep up with. I have since moved on to an Asus router (RT-AX86U) with the AsusWRT-Merlin software package. The only functionality I really lost was suricata for IDS. The AsusWRT distro comes with some proprietary stuff (that I think you can turn off) but it’s also very “open” in terms of just running Linux underneath. This means you can set up things like VLANS, use iptables, etc.

AsusWRT-Merlin adds some niceties (including a nice add on system that will expand into web based interfaces for certain things you might usually do from command line, better/expanded firewalling, and even adguardhome installer for DNS-based malware/spyware/ad blocking… kinda like pihole but lots of people like it better). The maintainer of that package corresponds frequently with Asus (to the point that some of his stuff is merged back into the official AsusWRT at some points).

I can confirm that the model I mentioned above is able to do all the firewalling, QoS, adguard DNS filtering, etc at gigabit speeds. It also has some sort of IDS and a few other protections, but they are part of the proprietary bits (Asus licensed via TrendMicro I believe).