Questions about Access Point U6-Lite

as of now have already ordered it

Almost nothing works without a controller, but you can also host the software yourself if you don't want to buy the additional device.

Hoi - I use two Nano in the cellar at a rather abnormal humidity (in a growth cabinet with 90-99% condensing artificial humidity and about 10-18°c) and one in the garage (current outside temperature and humidity, like in the garden) and so far the parts run like grandma's waffle iron: Stable.
I can't tell you if it's the same with U6Lite, but if the parts are reasonably safe from dripping water, it

It depends a little on the power, cat5e and cat6 are recommended for higher powers, but since these categories are now also old and new cables belong to a higher category, all current cables are suitable and only with very old existing installations should you check if necessary which category the cable belongs to and whether you need a high power cable at all (usually not, so this is also not a problem).

Unfortunately no. Must be purchased separately.