Search for "DSL modem" on shopee/lazada. If you want 5ghz then look for AC on the description, if N it only support 2.4ghz. I try search and unfortunately to tell you modem with AC is all above RM200.

For my case last time it is worth to get 5ghz support, as there's only Streamyx in my place all my neighbor is using 2.4ghz. During peak time my internet over wifi slowed down tremendously but if using LAN cable no slowdown. After research I found out because too many people using 2.4ghz wave at same time the signal affected badly. After I got 5ghz router no more slowdown.

I also have multiple devices that stream data over my local network, 2.4ghz maximum speed is about 5MB/s but usually more like 3MB/s because of interference from neighbor wifi, while 5ghz is 20MB/s, if 5ghz MIMO can go 40MB/s, 5ghz hard to suffer interference.

Another brand to consider is Asus. It is more expensive but worth the money. Last time I'm using N12, now got newer model N16, but these are 2.4ghz wifi only. What I do last time is N12 act as modem only while I get AC86U as router. Asus now got new model AX56U, same performance with AC86U but with WIFI 6 support and only RM400 something, it is a lot cheaper than AC86U. I would suggest you get AX56U or equivalent model, if in future your place changed to high speed Unifi you can reuse the router.

5ghz band is wider, so less congestion compare to 2.4ghz even if there's same number of user using the band. You can buy USB WIFI 5ghz adapter, there's size about same as thumb drive. wifi extender only if your device far away from router the signal not strong enough.

Too bad your router already bust, otherwise you can try stream data over wifi between your devices during peak hour and see if it can sustain 5MB/s, if cannot then too much interference from other people wifi.

USB 3.0 max speed is 640MB/s, 2.0 is 60MB/s, both is way over 5GHz speed.

Stream data over wifi between devices is such as copy files from laptop to your phone.

I'm using USB wifi, no stability or limit usage issue.

LAN or Local Area Network. If you have no idea what is this then it's not important for your unifi modem router.

It's about the size of thumb drive, there's no antenna on it. My computer is about 7 or 8 meter away from router with a wall between it. Still can get full signal strength. If more far away then maybe should get those with antenna.

It's a China generic make, there's no model name. It's been sometimes, the seller already put other item for the link.
But it's similar to this.
https://www.lazada.com.my/products/dreamall...s141032592.html

If you worry about signal strength then get something like this.
https://www.lazada.com.my/products/600mbps-...2307660226.html

My computer is about 7 or 8 meter away from router with a wall between it. Still can get full signal strength.

I want minimal look without the antenna sticking out.

Don't know, I didn't try other brand adapter. I only need one adapter, not multiple adapter.
2 or 3 years. I don't know will last how long.