I agree, I'll specify the number. Do you think 400 would be good/enough? My only intention is to make it fair for both sides. I doubt any project would need more than 400 icons. Unless its purpose is to distribute icons!
I suppose it depends on how complex a model you're willing to support. There might be some pricing opportunities available to you here, where a sliding scale can accomodate projects of various size. Of course, I could be overthinking the whole thing too.
Well, as its creator, I would say it's much better than FontAwesome in many different ways. But yea you can choose the icons you need, instead of loading one font with all the icons that you may never need.
If you look at the library tab (http://icomoon.io/app/#library) you'll see the free icon sets. There are also two premium sets available right now. These are different sets.