Hi! and welcome!
A good tutorial to start, for example:
https://community.openhab.org/t/speedtest-cli-internet-up-downlink-measurement-integration/7611
Yes, I know, there’s not much of the “physical” world in this tutorial, but it helps to get to know the system.
Please feel free to ask your questions about any control in particular
Yes, definitely for this you have to use rules, at the beginning it costs interpretation but you will learn (in my case I had no idea since I am an engineer but of a different specialty (chemical) haha).
I’m not so experienced but don’t be afraid to ask.
Good luck