iCloud should sync those automatically, if I read a book on my iPhone and finish a chapter, then I open it on my Mac, it usually opens where I left on my iPhone, and viceversa; or, almost at the same page, I should say, that's because the layout is different, so for example, sometimes I finish reading on my iPhone and I'm at, let's say, page 200, on my Mac I open the same book and I'm at page 185, so maybe you have finished one chapter on one device and on the other device you find the book a few pages behind.
As for marks, iCloud should be syncing them automatically.
The problem with syncing is that I don't think it's that instantaneous, I usually find everything synced because I read at night, then leave it and my devices do all their backups over the night, so the next day everything is usually synced; sometimes, though, I was reading on my Mac, then, shortly after, picked up reading on my iPhone and my progress was immediately synced.
I've yet to understand how and when iCloud works its magic.
I was thinking about getting a reader, mainly a Kobo because I wouldn't want to be tied to Amazon, I'm thinking, however, about the iPad, I like the Books app, I'm a little bit concerned about the iPad's size and comfort during long reading sessions, the Mini is just too expensive in my opinion.
