Well, if that's the definition of materialism then it's trivially false indeed. There are all sorts of things that exist conceptually without having energy or mass or occupying spacetime etc. Numbers, for example. But there's a little problem there, in that these kinds of things don't seem to cause or influence "material" events. Even consciousness is a tough one. I'm not particularly familiar with the literature, but from what I have read it seems like the growing consensus is that consciousness is little more than a byprodct of neurochemical processes and doesn't actually "do" anything.
Justify that. Sounds like an insane assumption to me!
I don't know, but that doesn't mean there isn't an answer! Or maybe they don't come from anywhere; perhaps they simply exist. Or maybe, if we concede that what's "good" is simply a function of the suffering/wellbeing of sentient creatures - and that suffering and wellbeing can be quantified in an objective fashion - we have an objective system without needing anything fancy whatsoever!
Because it would be moral to do so. That's what morality means! If you think "what is good" is equivalent to "what will get me to the afterlife" I think we're facing a grave misunderstanding of what morality is!
As above, this is circular. "It's the right thing to do" is a good reason. If it is moral to good (which it is, by definition), it doesn't cease to be moral simply because it won't get you to heaven.
But this rather presupposes that material reality needed to be created by something at all...
I'm not sure. But in physics, we observe strict causality in physical things (aside from the stochastic processes of quantum theory). So far as I can see there simply isn't any room for non-physical causes?