I would think your remote would have up/down/left/right/enter.
The OSD and everything in Theater View can be accessed fully with only those keys.
PS. Is there a keyboard shortcut to get back to the main menu quickly (Audio, Video, Images menu)? If I am deeply into the submenus of say Videos then it would be convenient if I could jump back to the main menu without having to backtrack every single step of the way.
In addition to the arrows and Enter (and Page Up/Down if you can add them to your remote), there is one other button you need:
F11 cycles Theater View. MC automatically assigns this button to the "green button" on WMC remotes, but it is also pretty essential so you should have one assigned to it on your remote.
It is a three way cycle: Theater View Home > Display View (if a file is Playing) > Theater View Last Position
This is designed to show music Visualizers, not Video, but it works the same way for video files:
https://vimeo.com/68349735