I’m familiar with the absolute basics of networking, but very little surrounding wifi.
I’m current using the modem-router-AP provided by my ISP, along with a couple repeaters. This isn’t working well, and in areas of my house further away from my main AP, packet loss is often around 20% - near unusable. How should I improve this?
I can run some wires (within reason), and have multiple spare routers-APs to work with. I can also buy something new off the shelf if needed, but don’t want to spend more than I have to. What would be the approach I should use? Like, is there a particular type of extender I should be using, or can I use multiple routers as a mesh or something?


Instead of chaining them together, try to put the “router” in a central location and do what’s needed to limit your repeaters to a single hop away from the router. Chaining them together will lead to problems.
A proper mesh system will work better than repeaters. Some systems can use powerline networking to use your existing power outlets as a network, but it’s not always that great.
Some locations such as apartments/condos have really bad interfering neighbors on 2.4ghz. If that’s your situation then using 5ghz exclusively might help.