My question is if the leaf knows that Orchimaro is head of the sound village why don't they just send in a platoon and take it out. I know they don't have the resources now to do something of that scale but what about the other main Ninja Villages? Wouldn't they also jump at the opportunity to take down a wanted S-rank criminal?
Not neccesarily, the other villages wont attack the Sound, because they know Konoha is under attack from them, wouldn't they rather a big village to go down instead of a newly developed one. Also they will say that it's not their fight with sound, wait till Konoha is even weaker than it is now, but other villages may know that the treaty is on with the Sand Village, and better than ever.

Now you might say well now Village #1 will rather take out the Sound because it is smaller village and it's taking on a big village such as Konoha. I would say Konoha have more enemies and more known for such power they had, but also that they made Sound and Sand retreat back to their villages, and they put up a good fight, they may have lost quite a few of their ninja's and the Hokage, but they still held off 2 villages and a ninja known as a Legendary figure and S-ranked criminal.