Aaww you can't be scared to ask questions **snuggles!
Infusion has a 10m range. It doesn't say it in the description but I've played around a little bit with it, and 10m sounds about right.
If you're not in combat and cast a heal, you won't proc infusion on anything even if you have a mob standing right next to you. If you're in combat, infusion will trigger on the mob closest to you in a 10m radius, even if you're not in combat with that particular mob.
And yes, if you have a mob rooted and infusion procs on it, it has a chance to break the root, just like any damage you do on a mob. Stuns aren't affected, but you can break a mez with infusion if you're not lucky with your positioning.
I'm pretty sure that sums it up
