All of my remote routers are running RouterOS without anything on top of it. RouterOS is powerful enough for anything I throw on it. But I am using much beefier routers, I have 2 x 5009 and a HAP AX3 which have plenty of flash and ram ro run the additional packages I need.
As for normal computers, I have it on a UPS and I backup core files to off-site areas. Additionally, I buy SSDs that have a little bit of powerloss protection.
I've never had issues with mini PCs but I've had issues with PIs. I've since switched to high endurance SD cards for my Pis and they've been rock solid. One's actually semi exposed to the elements for about a year now without a hiccup.
With RouterOS you can still use DoH with either a self hosted list or a selected ad list. If you want to selfhost a DNS server I'd just host a Adguard Home instance on a VPS for all of your devices.
I also have 2 VPN system for my remote management on 2 separate systems. I learned that the hard way when one of my clients is 8 timezones away.
RouterOS has WG built in as well as ZeroTier. RouterOS has become quite powerful lately, but make sure you have at least an ARM/ARM64 CPU for it.