Anyway, sorry for editing my last post so many times. Spelling, reading the pathfinder SRD, etc.
I'd recommend going cleric as your third or fourth level. With 10 Wis, you'll only get the orisons as a third level pick, but either Stabilize or Virtue is fine. Grab any other you want. The real power of the multi-class pick is the domain powers. And a wee bit of healing if you want to help your warrior types. Travel, or Travel(anything) is good, because there are so many abilities that ninjas or rogues use that require positioning or base speed (or enhanced speed). There are a lot of situations that are considered difficult terrain in Pathfinder, so just basic Travel may be the most useful (although, looking through doors is cool, plus it gives Expeditious Retreat rather than Longstrider). Trickery(Deception) is friggen awesome, and lets you utilize battle tactics that would be considered broken in any other game. Even "wait" options make this good. With any type of party coordination, if the enemy misses, you can flank (and potentially ninja trick or sneak-attack them to death, 3 times a day).
If you choose this at 3rd level, you get a bit of healing, some handy domain powers, some mini-spells and nothing else. As soon as you put a point into wisdom (at fourth level) you become a ninja god. You can just as easily (and more powerfully) choose another level of ninja at 3rd level, and then point into wisdom and be a Travel + Trickery(deception) cleric at fourth. Either way, ninja god. It depends on how you want to RP it. +Sneak attack damage, or situational goodness.
It's not a horrible idea to level into cleric once or twice after this either. Length of spells = good. There's also the "big battle" option, being Anything + Magic(divine) domain. Probably Travel(exploration) or Trickery(deception) with the magic domain option. When you cast Expeditious Retreat/Longstrider at the start/middle of a battle, it's a Kiiiiiiiiiiii!!!!!! rush for your party. Pretty cool. Works with heals too. Any divine boost, plus extra boosts for a turn.
Anyway. Sorcerers are easier, but clerics are awesome. Very awesome.
ALWAYS make sure your wisdom is higher than 10 in Pathfinder, just in case you want to take a level of bad ass.
edit: yep, edited again. Next time, just make sure you have 12 Wisdom, heaps of Dex, and multi-class however you want. After reading the ninja class, I'm still not sure of the ki points of everything. Meh, whatever. A lvl 2 (1/1 rogue/cleric) would still make a better ninja than a lvl 4 ninja. It's even core-rule-book-a'fied. Without barely-used-weird species or classes. It's more broken as a leveling ninja/rogue with that lvl 2 cleric boost, regardless of foxes and stuff. Just make sure any character has Wis 11+, learn to RP any annoying situation the GM throws at you, and feel the power. Clerics>Sorcerers. As long as they're allowed. Sorcs are easy to fit into any world though.