To install the stock image, just write the downloaded image to an sdcard and boot with it. From there it is just standard Openwrt configuration for your needs
Yes, I use TP-Link UE300
As I wanted to run lxc, i built from the sources using the guidelines in the image building section. A reasonably powerful computer running linux is required to do this.
I use a Raspberry Pi 4 2GB version. Have dual FTTH connections and both of them are connected to 2 nos. of UE300. The integrated ethernet connects to a managed switch with VLAN configuration. A WiFi access point is connected to the switch. I use mwan3 for failover and loadbalancing over the FTTH connections. SQM is enabled on both wan interfaces for traffic shaping. LXC containers are created for running Pi-hole (DHCP & DNS) and Grafana (monitoring)
The Pi cpu usage is very minimal (typically less than 5%). Memory usage is below 500 MB, so this should work with Pi 3b 1 GB very well. My friend recently migrated to similar setup and he is now able to saturate his 300 Mbps Fiber connection easily
Faced the same issue, the resources are scattered all over the place. There is no one guide which explains it all.
It is not too complicated once you get a hang of things. If you have used Openwrt before this should not be difficult
Bobby