Pictures please.

The only room you don't have an idea book for! Start there. Houzz has several good articles about small bathrooms. For many years 5x8 was a standard sized bathroom, so lots of threads concerning that size that could be incorporated into yours.

I definitely would recommend a mirror in the bathroom to give an illusion of a bigger bathroom also a pedestal sink would be nice.

Look at as many pictures as possible and save those which you find immediately appealing.

Once you have accumulated enough, there are probably going to be some elements that are common to your inspiration photos.

At that point, you can think about how you would bring your inspiration into your actual space.

My design book shows this 5' x 7'6" bathroom. Since your bathroom is 10' long, you could extend the vanity to the right. All the plumbing would be contained in the same wall, simplifying construction. A floating vanity and light colors might make the bathroom seem larger. -- amateur