thank you very much for welcoming me and your quick reply!
The mentioned book from Liz Castro maybe is the right choice for me. I'm just worried about it's content in actual context. Liz published the book in 2011 and I assume that iBooks got updated since then a hundred times. Liz already blogged it some time ago, that functionality varies from update to update. That's what an update should do, but in my opinion more under the aspect of adding features, than of dropping them. However ... I'm not sure if the - for sure genious - book is up to date regarding to my special interest in page breaks. Maybe I will give it a try.
Thank you again for reply!