I have a Square Wedding Cake due in a few weeks, need to get the ribbon soon. What size typically looks best? I was thinking 1.5", or should I go bigger?

I like using 1 1/2 " ribbon.

What is the height of each tier typically? I personally don't like to go over 1/4 of the height, unless it's a tall cake with multiple tiers... and the difference between tiers is 2-3" since that pulls your eye upwards and makes the cake look taller. It's an asthetic's thing and the sizes of everything can really change how your cake looks.