yes you can have alagea eaters in with the exos they do not mess with them i have a cray fish in with mine to clean up all thier scraps. they don't go to the bottom to pick up food
I don't think dwarf puffers will do very well in such a large tank because of their relatively small size (about 1 inch). They are so small, they can be picked on by other fish, or they could themselves be aggressive terrors who will stress everyone else in the tank. Also, it will be hard to have them all to have enough food in such a large tank, and they will be very difficult to see. It's best to keep them as a species-tank only fish, and most people aren't willing to use such a big tank for only dwarf puffers. Here's a great site about dwarf puffers: www.dwarfpuffers.com
For suggestions, I think a pair of moonlight gouramis would look great in a 72 gallon. Here's some pics:
im still gunna say that a dwarf puffer tank owuld be cool and they get along pretty good with ottos and there great algea eatters. from the research iv done i really do think its a possibilty to do a DP tank that big you just need to have the right ratio of male to females to keep down agression. and winter wind he wants a species tank.
If, like every LFS I've visited that has them, by "vampire tetras" you are referring to Payara (genus Hydrolycus), then that is a rather awful suggestion. They require good current and very well oxygenated water. They're all but impossible to wean off of live food and are very inactive during the day.
All of that would make a fine fish for some people, but did I mention that they get a little on the large side?