I would say try to mix and match Crit/Haste gear until you have ~20% Haste, then go Crit/Mastery. As for Gems I would say if below 20%, a mix of Crit and Haste. Above 20%, full Crit.
If you want to do a preliminary look at what to expect, you can use Wowhead's Profile. For example, this is my character and you can get a general idea of what your stats will look like:
http://wod.wowhead.com/list=38675/us-kiljaeden-delritha
One other thing... You may want to look into getting Cata food/flasks. Due to the stat reduction, quite a few of the older expansion consumables/enchants are giving more stats than the MoP equivalents. Such as flasks, and food:
http://wod.wowhead.com/item=62669 vs http://wod.wowhead.com/item=74648
Even enchants are looking to be pretty good:
Mongoose - http://wod.wowhead.com/spell=27984 compared to http://wod.wowhead.com/spell=104434
Executioner - http://wod.wowhead.com/spell=42974 compared to http://wod.wowhead.com/spell=104425