Hi,
i fiddled with iBooks for a while now with iTunes 12.7 and iOS 11. It really only works as McPoodle states above. An alternative is to go back to an earlier version of iTunes 12.6.x, but that really is only a stop gap measure and I don't recommend it.
I suggest trying out other ebook readers.
You can try both Marvin 3 and KyBook 2 which are the only full feature readers I know (would be glad to hear of others). I bought both to try them out and report here:
Both offer all features in the free version but have advertisements. KyBook costs 4 Euros, while Marvin costs 5 Euros to get rid of the advertisements. Both have pretty much everything you need. KyBook offers some extra features but also adds some complexity in the settings so Marvin is a bit easier to use.
Both can get Books added via iTunes (click on your device whilst connected) via the app add files option. Both offer adding of books via iCloud or other systems. KyBook is
especially open to different methods.
I can recommend both KyBook 2 and Marvin 3. 
I chose KyBook for myself,
because the reader is a bit nicer (subjective) and library view has more options, I especially like the icon view with text under the books. Also it reads more formats than Marvin. Here is
another comparison.
KyBook TiP: in the "Synchronization" settings, turn on "on the Device" to see all the nice book covers in the "File" view.