Well fortunately I've got a 180 gallon with all of the aforementioned fish in it already minus the barred midas.
I think I'm just going to let him take up the entire 100 gallon as his own home and leave the other fish as is.
I will be adding the pleco, lap. bichir, and some dithers, though.
My lap. is 12"+ and everything ignores him in the 180 gallon - though the pike used to pick on delhizi it could fit in it's mouth (I'd find the pike with half a delhizi's rear end in it's mouth and the delhizi fighting to swim away all the time). So it's probably a better solution to remove the bichir before the pike gets too old.
I'll throw the oscar in there and monitor em' - if too much chasing starts I'll just remove the oscar back to his 180 gallon with all the other fishies.
Yeah I was going to setup a 120 - but it sprung a leak and a giant crack went down the back, so I have to settle for my 100 - which is too bad because I think the extra 1 foot of length would have made the oscar/midas combo a for sure thing.