For me, the idea of having the book, plus a changing background, plus the bottom UI, is just overkill. If you want to have the book, you need a better solution to the main RPG UI, that's integrated more into the theme - you could have a form lying underneath the book, or something similar. I'd also put the book into context - flying book looks weird, but it should be easy to have a nice desk background - take a photo of some polished wood + some props, maybe use a few filters (judiciously) and you could have something much more consistent. An archaic dashbroard with valves etc could also work, but not as well I think, at least with the book design. I know you want to indicate time with this, but something more subtle like a changing sun/moon illustration integrated into the book could do this in a more classy way. Alternatively, you could use the entire worldmap as wallpaper behind, with just the fringes visible around the book.
More concrete nitpicking, I think the book design is mostly ok (faint praise I know), but I'd put the room name at the top of the description myself. Do away with the permanent stat view below, unless the player is always interacting with it, and just have a character dossier slipped in to the front of the book that the player can flick to at any time. (Rage, Fear and concentration probably need to be visible at all times, though, so you might need some sort of gauge there) Put the compass windrose at the bottom of the left page (hell, even find/make buy a nice image of an antique compass and use that layed on top of one corner of the book) How will you handle the player's log of route taken / actions performed? Maybe consider putting the current room on the right side, and the log of previously visited locations and conversations on the left? Eyes flick across to the right more naturally. You can always have this section divided into three parts - the basic room description, permanently visible, a detailed examine/interact description of items that can be interacted with, and finally the interaction prompt. How will you handle interactions as a CYOA hybrid?
As for the inventory, I think a text inventory would work better, but the current layout is a bit muddled - the left side are tabs for sorting stuff, right, but the heirarchy isn't strongly suggested. In an object-puzzle base adventure it's probably best to have it always on screen, but it's not necessary in a dungeon crawl RPG - maybe a few slots where you can drop useful items, weapons and tools that are permanently visible, the rest goes with the character sheet.
What's your combat interface? Pure text? Old-school graph paper grids and abstract symbols for characters?