I would recommend installing opnsense on any old desktop PCs you have lying around. Get an intel LAN card with two ports (or more) and you'll be golden.
OpenWRT is fine but I've found that if you're shopping around for devices it's hard to find ones that will do 1gbps with traffic shaping enabled for an affordable price.
ServeTheHome has been doing a series on fanless mini desktops that are perfect for the role of router (most don't have WiFi though, you'd need a separate AP).
Honestly, not such a bad thing. Routers are normally located far from the ideal location in most houses/apartments for good wireless coverage. Usually in the corner of the basement where the coax/fibre/phone lines come in, not exactly a good place to put an AP.
I've been running separate APs for awhile and IMO it's the way to go if you're at all interested in running anything like openwrt/opnsense.
Modern routing appliances are like a vcr/tv combo. You will have a better time if you split the functionality apart. It allows you to change/upgrade pieces of your network infrastructure more easily.
For sure - I casually looked at OpenWRT on x86 and it seemed (on the surface at least) to be more fiddly than opnsense. Updates and handling storage/partitions appeared to be more unclear to me. But that was probably just me, I didn't dig too deep into it.
1. Use the ext4 image and extend the main partition to the full size of the disk. This requires a lot of "fiddling" later in case of upgrade (as parent wrote).
2. Use the combined squashfs image and don't touch the image layout (no resizing, keep the ~100 MB free default / partition). Easy upgrade experience like other embedded devices (get image, open ui or ssh, upload, flash, reboot, done). Oddly, this isn't made clear by the official Wiki at all and the simplest option.
IMO, the best configuration is running your x86 box with Proxmox and run the squashfs OpenWrt in a VM. There is no need for more than 100 MB of space and if you need to install so many packages or apps, better create another VM and use a standard Linux distro. It will also be more standard for many apps to be installed on a full fledged OS instead of the custom OpenWrt layout.
You only need 2vcpu and 256 MB of ram to run standard OpenWrt at 1 Gbps (SQM included if you have a recent CPU). The rest of your box ressource can be used for anything you want.
I used to run OPNsense but I switched to Debian because of https://news.ycombinator.com/item?id=34839161 . I wouldn't recommend OPNsense any more for anyone who cares about security.
OpenWRT is fine but I've found that if you're shopping around for devices it's hard to find ones that will do 1gbps with traffic shaping enabled for an affordable price.