1) Buy another wireless router and connect it to the LAN wire that you are having right now.
2) Locate the wireless router somewhere to a location that is probably the best to serve whole condo and connect it through LAN cable.
3) Locate the wireless router somewhere to a location that is probably the best to serve whole condo and connect it through PowerLine adapter.
4) Buy another wireless router and connect it through PowerLine adapter.

The 1 and 2 give better throughput performance, most likely.
The 3 and 4 is neat because no wire cluttering the condo.

The best of both solution is to buy mesh router. You can locate satellite unit for best whole condo coverage.

Yes. Why not? If not sure how to configure, copy the router in the hall configuration and use different channel.

I don't use Maxis but I think the BTU is the one established the connection to Maxis service. The router in the hall has gateway which is the BTU address. The router in the hall has its DHCP enables to provide IP address to devices that requested addresses.

The 2nd router also need to have the DHCP enable so that it can provide address to its clients. The gate way for the 2nd router should also be the same gateway as 1st router.

Both router is not dialing for service as this is done by the BTU. The BTU convert the optical signal to electrical LAN signal. How many port on the BTU? If you plug in the 2nd router on the 1st router port, then the 2nd router will have the IP address from 1st router. This way the gateway for 2nd router would be the IP address of the 1st router.

I hope I'm correct. So long not playing with this

You already have the 1st router working. To manage this router, you need to type an IP address, right? This IP address is the IP address of this router.

Where do you connect the LAN cable? Is it at the back of the 1st router? If this is true, then the 2nd router get the IP address from the 1st router.

Therefore, the gateway for the 2nd router to access external connection is the 1st router IP address.
The gateway for 1st router to connect to external world is the IP address of the BTU.

You get what I meant?

Looks like you don't know much about networking.

I believe your LAN cable you are using is connected to a LAN port on the 1st router, right?

Do you know the IP address of your 1sr router? This IP address is the number you type on your browser to access your 1st router.

The best way is to get a friend or neighbor that know how

I'm afraid the using power line is also like replacing the LAN cable with power line. You will have the same problem. It is not Plug n Play

Range extender is the simplest because it is just extending the rf signal from existing WiFi router. Then you will have strong signal in your room at the end of the condo. This is Plug n Play.