Here is a link to the new add on makers toolkit.
Learn how to make new buildings and tons more for Sim Settlements 2!These guides and resources will teach absolutely anyone, regardless of their experience how to create or inject content
www.nexusmods.com
All of the Bethesda Mod School stuff I watched from KG still applied since the CK hasn't changed since I don't know when.
Additionally I recommend requesting access to the SS discord so you can better talk to other creators who can help if you come across any stumbling blocks.