Towel ring and toilet roll installation dilemmas. Help!

I finally managed to find and purchase a towel ring and toilet roll holder that I liked, for the downstairs powder room. But being the person that I am, and making a big deal over every single detail... I am putting off their installation because I am not sure where exactly to fix them.

What is the optimal height/distance from the back wall for installing the toilet roll holder? What about the towel ring, should it be in the center of the width of the vanity with the folded hand towel hanging 3cm from the top of the bench top? Or should it be closer to the front of the vanity?

Raymor Boston Towel Ring Chrome

Raymor Boston Toilet Roll Holder Chrome

Do you think the fixings they came with are secure enough? I have a fear of them coming loose and falling off... :(

B