The 1 re: upkeep is brutal! Too brutal actually :'/ because it's 33% odds of devouring with Yog. Make it so that it's rolled during the mythos phase for investigators in the first area of the Other Worlds (the second area would be even scarier, but, you'd have to address find gate).
And of course all your fixes would work fine also ;') Especially all investigators must discard a gate.
How about that, and +five doom, I guess what I'm a bit worried about is if the DH awakens, the doom track's going to be so high no one will bother to kill it because you're practically at final combat already. There needs to be incentive to kill it (i.e. penalties for not killing it).
Gtg.