The best thing you can do is love him unconditionally, support him every way you can, and encourage him when he's doing well. Funks/depression are internally regulated and internally self-sustaining. If he veers in a new direction that strikes you as even a tiny bit positive, encourage it. We can't dig others out of their own holes. All we can do is let them know there's a loving world outside.
Yeah, sounds about right. Whenever I try to help I fear it comes of more as "why haven't you done this yet" than the "let me help you out with this" that I intend. I'll let him figure it out on his own, hopefully he does :) It's mostly being unfulfilled work-wise than anything, so maybe being encouraging of the side-projects will help!
Good call. Because he isn't stupid. He knows he is in a funk. So your offer to help will go through his internal filters and be translated as, "You are a failure, and even I can see this, so you need my help." And he is not where he can hear your help for what it is: A genuine expression of love and support. He will hear it as an attack. I know from experience. This is what ended my first marriage.