And I look at compatibility matrix before buying it.
This strategy has worked very well. I upgrade on my terms.
I agree in the abstract, but I've seen enough devices ship OTA updates that make switching harder that I prefer to just cut over ASAP these days. (This is a general approach, not just for network gear; same as how I unlock my phone bootloaders right out of the box so I don't have to deal with data wiping)
Something like https://pcpartpicker.com/list/3MpGmk
Some people don't care for Realtek nics, you can spend more to get Intel if you want. You could put more ram, or storage, or whatever if you're going to do more than routing. Ryzen might be nicer, but they don't have a cheap CPU with integrated graphics right now, and it's not worth paying $100 more to get one for a router, IMHO. If you can find a motherboard with IPMI for cheap, that'd be nice, but I can't, so I just use a spare monitor and keyboard when I need to.
There's small x86 router boards around, and they're cool, but if anything goes wrong, your options are limited. If anything in this fails, you can get the part replaced at your local computer store, even if that's BestBuy.