Hey bees!
When creating or editing an object, if you right click the Category textbox, you may choose from existing categoies.
For the other issue, I suppose we have the "Exclude" and "Scrap pile" options. For objects you do not want to link, you can exclude them by the checkbox, or simply define your arbitrary terms / phrases in settings.
Also, no discord server I'm afraid. Although do not hesitate to come up with suggestions!