1) dedicating a button solely to start / activate XBMC: 
a) go to Prefs > Mapping > Global mapping 
b) choose a button you want to use for starting/activating XBMC and *nothing else*. 
c) select the action "Behaviours > Activate XBMC Behaviour" for that button

2) always open the menu at root level 
a) go to Prefs > Mapping > Global mapping 
b) for the Menu button, pick the action that opens the menu at the root level

3) long-press left when the RB menu is open to jump right to the root level of the menu

4) create your own menu profile and place the XBMC item where you want 
a) go to Prefs > Menu 
b) press "+" and select a profile to start from 
c) select the new menu profile and press the checkmark to make it the active one 
d) use drag and drop to add new items 
e) add the "Behaviours > Activate XBMC Behaviour" to create an item that directly starts/activates XBMC (saves you the extra step of choosing "Activate Behaviour")

Best regards, 
Felix Schwarz