Hi Marnie,
I'm pleased you managed to get the fonts you wanted.
There is a way to change most sizes and it is possible to change from an A4 to A5. Bare in mind, that A5 is half the size of an A4.
The way to do this is to click on Book, then on Functions, then on Change Book.
If you just want a plain colour on the background, just right click on the background and choose, Change page colour. If you want to do custom colours, then select this and you can also change the lightness by dragging the slider up and down.
If you want to add it to custom colours, then make sure you click on an empty box under the colours, then find the colour you want and click on "Add to custom colours".
I personally don't care for black backgrounds. If you do choose this, then I suggest putting a white border around the photos to enhance them.
Regards,
Suzanne