The documentation looks to be complete on this, but creating items is second nature to me at this point! What information do you need? I personally use item files, since I was familiar with them from OH1. The thread I linked to has examples of my items, so you can just copy them into a text file that uses Unix EOLs and save it to the right location. OH will immediately pick up the new items, but I prefer to have OH shutdown when saving items files to avoid issues.
No, there’s no need to format the OS or to reinstall OH, because that would still not remove the ghost nodes. The easiest way would be to exclude the devices and then reset the zstick (turn off OH, unplug the zstick, hold the button for 20s). Another option is to use Zensys Tools, which Aeon Labs looks to have stripped down as their OTA firmware installer app.
It is also distributed with the InControl software by Axial, but they have a link to download it too.
Using Zensys Tools, you’d send a NOP to the dead node (you have to type the nodeID into the text box). This should fail, but sometimes it takes more than once. Select the dead node. Click the IsFailed button to check it. This will mark the node as failed. Then you can click the Remove Failed Node button. It sounds daunting, but is a good thing to learn for maintaining the network in the future. The worst thing that could happen to you at this point is that you’d have to do a reset. Better to learn how to do it now than when you have more devices on the network. There may be some more detailed write-ups on the forum.