Always good to see others trying it. I’ve been a user since the 80’s. KeyCreator 10.5 that we are using is extremely powerful and compared to CK98 it will be like working in another universe. Support is good but not as responsive as it was when they had the dealers but still it’s pretty good. As far as 3D vs 2D, I’ve always done my work in 3D, even when it was just wireframe. So I can't say anything about the learning curves. I think each individual will be different. They have plenty of online help tools now that should help a lot.
When adding features or fasteners such as holes or bolts you will have to set the CPlane (Alt-Z) to match the face where you want the bolt, screw, hole, etc. to go. Just hit Alt-Z then select the face or planer set of entities. To toggle though the faces, hit the space bar.
I think the tapped hole command is just to show a representation of a tapped hole with no threads. Not sure why you’re getting the error but may have something to do with the setting for that particular situation. Solid tapped holes showing threads I don’t do. I find them to be overkill and a waste of computer resources. They can really slow down even the most powerful systems. If needed you can do these by Boolean subtracting a bolt or stud.