You would do well to go through the Getting Started Tutorial to refresh your memory on what you may have forgotten and get introduced to the new stuff in OH 3.
At a very high level:
Install the Sonos binding
Discover and accept the Things that represent your Sonos devices
Link the Channels of those Things to Items
Your UI (HABPanel I suppose) sends commands to these Items to cause Sonos devices to do something.
The same steps go for Tradfri though I’m not aware of a Tradri binding.
Do you really mean HABPanel or do you mean MainUI?
Yeah it is a painfull and long road for being usefull for me yet.
Sometimes some out of the box solutions which can then be changed and tweaked, is better than a clean sheet. Alas OH is my only option having an old iOS 9.5 tablet destined to use the HABPanel as that one still works flawlessly on such an old safari browser. No other Open Source solutions has yet been able to work for me.
I have now a basic Sonos house control with HABPanel, using two community widgets, and two “standard” widgets. It works rather well and is working on an iPad mini running iOS 9.5. So this gives life to older tablets still. YAY!