I was wondering what the 'challenges' and faction ranks do for me. So far I can only see that I get a small discount from hiring them all... Though when I have 50k at any given time, this is a rather useless perk for doing all the extra bits.

So far, I only do the challenges because it's a neat little bit to change up playstyle to mix things up a little. Beyond that, I don't really get it?

(And I could have sworn I've sent like 5 teams of courtesans onto guards but the counter is still at 2. I don't get that, either)

I think that you get specials weapons and gear for going them. I think Thieves gives you a dagger, Mercs a greatsword not, not sure what you get from Courtesans and Assassins.

AvauntVanguard:
So far, I only do the challenges because it's a neat little bit to change up playstyle to mix things up a little.

That's pretty much it. They're meant to be optional missions you do for fun.

This wiki article explains it. It has a full list of the challenges, and what the rewards are.

Oh snaps. I have Altair's sword and I didn't even know it O_O

Thanks for the link.