i agree with baamnyc!
The hippo will get way to big for your tank fast. If your heart is set on one, get a tiny one, and be prepared to re-home it in a year or so. All the other fish on your list are fine. The midas blenny happens to be my absolute favorite of all the blennies. Just make sure that you get a midas, and not the canary blenny. The midas has blue eyes, the canary doesn't.
As to power heads: If you have the cash (i don't) then the vortex with the battery backup is the recommended one. Next to that is the tunze, but if that is still to much then go for the koralias. I have 4 #4 on my 155. Two is best for your tank, point them at each other to create some randomness. Their flow will crash into each other, and spread out a bit.