This is going to be very difficult. You are going to need good STR, DEX, CON, and WIS. Many of your monk abilities are not going to work while you are raging. Check with your GM to see what is allowable. I could see a GM saying you cannot use your Ki pool while raging. If that is the case you will probably want to reconsider doing this.
Saying you want to be a barbarian/monk is very non-specific. Why do you want levels in barbarian and monk? What do you want the character to do? Mechanically.
Single class characters are more powerful than multi-classed characters. The exception to that is when you multi-class for a purpose. Identify the purpose and then lets see if we can build an idea character to fulfill that purpose. And there is a very, very good chance that the finished character will not be a barbarian/monk.
Especially considering that Monks must be lawful or they become ex-monks, and Barbarians must be not lawful. So that means the character is capped on one of the classes and possibly can't rage.
So back to the big question: what do you want your barbarian/monk to do? Is this a grappler? Is this a punching guy? Fastest runner in Galorian? Why that combination of classes? What should that do for you?
The martial artist archetype is probably probably the least painful way to combine those two classes. Martial artists can be of any alignment, and most of the new abilities they gain in place of a ki pool are static or passive abilities that won't be lost while raging. (Exploit weakness is probably the most notable exception.)
But in general, I agree with the other posters above that what you want to do with the character will determine if barbarian/monk is actually the best path to your goal. To give just one example, if you want to furiously tear people apart with your bare hands, a brawler might be a better choice than monk. It has similar damage output with fewer restrictions on alignment and armor.