You will need to switch combat reflexes for combat expertise if you take improved trip at level 1. That requires an intelligence of 13, which is a heavy investment for what is often a dump stat with monks. A lot players will wait until level 6 when they can their monk bonus feat, as these don't need any prerequisites.
If you do stick with the combat expertise route, you should know that greater trip will stack with vicious stomp, as confirmed here :)
http://www.d20pfsrd.com/feats/combat-feats/greater-trip-combat---final
