How to expand Wi-Fi coverage?

Question

WiFi

Given a two-story house that has a GrooveA 52HPn access point installed on the ground floor , it covers the entire first floor perfectly, but does not provide normal coverage on the second floor. Therefore, it is required to strengthen it there. For these purposes, I plan to purchase Ubiquiti UniFi AP-LR and install it vertically on the wall.
From here questions:
1. Whether the second access point will be a good choice?
2. How to teach them to work together so that when moving from the second floor to the first, the connection does not disappear and the network bandwidth does not fall? (the cable will be led to both APs)
3. How important is it to hang the AP from the ceiling or hang on the wall, does this affect the signal quality?

Answer 1

You need to give one sid to the access points, and hang them on different channels, transparent transition will not work very well, but users will not notice.
Seamless roaming will only work with WDS and not using EAP

Answer 2

@Yekver
1.points will interfere with each other as they won't know about each other's existence.
2.configure them one network with the same parameters.
3.Get different polarization. affects.

Answer 3

Isn't it easier to install a repeater in the form of a router?