buttons in windows 8 app bar
The app bar is made to hold 10 commands in any direction with the recommended padding.
However, with the handheld devices it can get a bit tricky to press the buttons in the middle of the screen (if you hold the device with both hands for example)
So try to narrow it down.
How to do that? well here are a few suggestions.
Start with listing all possible commands for your app (one page at a time)
Group all similar commands – in this case everything related to the view and filter. You don’t need to use a divider, but you have the option to.
Use flyouts and menus where appropriate – this example only shows one filter button, but all 3 is shown in the menu. A real space saver.