I am a new (less than two weeks) TiVo and Roamio Pro owner. I have a lot of questions about the user interface too. I had been trying to figure out the remote control and User interface by myself too. Luckily, if found a document "Viewers Guide for Roamio Series DVRs" on the Tivo website. It has helped explain what the remote buttons and menu options are meant to do on the various menus.
Yes, there is a way to get rid of the "thumbnail window" in the upper right corner and give yourself 6 choices across the top instead of just 4 across the top. I tried this, hated it, and reset it back to the default.
This PDF document can be found at: