What should I consider when using Wi-Fi?

If you don't have heaps of metal nearby, it really doesn't matter which position you use. Red green blue, it will hardly make a difference.

Regarding the terrace. We have 6 neighbors here, all have standard Telekom 1&1 devices, etc. I can see all the networks here at my place (with acceptable performance) and I can also use my network when I am on their terrace.

As long as it only concerns 2.4 GHz, you don't have to worry that much.

I unfortunately do not know it, but as it appears on the manufacturer’s site, it can also be installed close to the ground. It’s best to take a look at the ubiquiti page.

We have an outdoor access point from Ubiquiti and are very satisfied with it. Perfect Wi-Fi throughout the entire garden. The access point is mounted on the garage using an antenna mast.

The permeability of the walls varies from structure to structure. I was surprised at how signal-dampening our wooden walls with cellulose insulation are.

The permeability of the walls varies from structure to structure. I was surprised at how much our wooden walls with cellulose insulation attenuate the signal.

In our current rental apartment, I also notice it strongly, same floor, 2 rooms away = hardly any reception, of course there are 3 walls in between (without a corridor).

The existing current WLAN threads are still high enough in the post overview, so I will not link them separately here.