Ah, I see. Well, I suppose that he could, after some time, leave bits of himself behind as the things he consumes simply becomes Biomass for himself. Thinking pooping. Additionally in a gameplay sense, imagine that instead of having an MP Bar for his powers, they all come out of his HP Bar. He has a set max, but his standard is usually never actually at the max unless he takes in the required mass. HP in this instance not actually being Health Points but Hunger Points; when it is near max Damon isn't hungry, when it's low he's starving, etc. The more he creates the more hungry he gets, so at some point he has to stop creating things else what he kills starves to death. 

As well with the Conversation, while he isn't quite certain what the rates are, there is a general rule of thumb that if he wants to create something he needs to get the right material first. So while he can't turn lead into gold, he can at least turn a bunch of lead pipes into say, a lead slide (Assuming that he has eaten both pipes and slides in his past). Now he can do things such as extracting what little water he can from say, a cactus, but that's under the impression that there was already water in the cactus. He didn't make water out of the cactus, he just isolated it from it's source. Though I should let you know that when Damon becomes much more powerful, this Conversation will also allow him to transform matter into a different type ala Alchemy. The Conversions, while still unknown, are much looser, allowing him to potentially create the water into gold example. Not something he can do right now, but one day when he isn't just a minor demon.

Damon is still fairly young despite being over 70, though I don't imagine that the Underworld is a very great place for educational pursuits and he's only achieve sapient for maybe twenty or thirty depending on how you define sapient. That and by young I mean that this isn't even his strongest form; as far as I know about the demon hierarchy, he still mulls around with Imps and such. Hence why he left; to grow and become stronger. 

Also I know that the accident is likely an isolated case (Unless things get really bad later on). The Angels themselves aren't part of any large nefarious organization, just a local threat at that time. Though since they did have knowledge of the Revenge Cycle and there was a survivor, time will tell if Damon meets them again to collect on his debt.

And also, Damon and Noel will be traveling together. That's what I'm writing right now, their adventure of how they met and what they've been doing. Addendum: Where is everyone at? I want to make sure that Damon and Noel are within the area so I don't have them just bumming around themselves.