Good plan! Uthal can offer up 'Pass without Trace'. Which will give us a bonus on stealth. Might be worth a look in for those ambushing the ambush. He has a few other druid tricks up his sleave also, should they find a place in this mission.
The only hiccup I can see with the plan is we need to know where the bandits will strike. Unless the hidden party members secretly just follow the disguised party members until they are ambushed. As we don't really know where they will strike, that seems a might risky. Or we just go out, set up camp and wait in the hope that our treasures look inviting enough.
Sorry for the lame game post. Be good to get back on the road and into some trouble.