Adobe Illustrator size change and filling of size background

I have created a children's book. The text has been inputted into the illustrations and all the pages are ready on Adobe illustrator.

For various reasons, I now want to increase the size of the book without changing the size of the illustrations and text. I.e keep the current images that include the text at the current size, but increase the size of the book. This will mean there will be empty space on all four sides of the book that I want to be filled with the right colours, according to the individual pages.

I also need the pages numbered correctly and designed in a way that suits the book.

Lastly, I need the book to be ready for print via pdf.