I'd shy away from the Butti. They tend to get super aggressive and will more than likely kill a lot of your fish. A LFS near me had a Butti with two 13"+ Oscars and about a 17" RTC and it ended up killing one of the O's and injuring the other two fish pretty badly.
Definitely no butti, everything else might work depending on the fish. I had a small tank that had half a dozen rosies in it that were there to keep the cycle going. I put a 3/4 inch butti in there and didn't take the rosies out right away because I couldn't catch them. An hour later 4 rosies had they're eyes ripped out and were floating. I have never seen a nastier cichlid. Very cool when adult and in they're own tank though.
True. I'm a little worried a festae, jag and Midas getting along in a 300. Festae in a 180 could be tough. If it were me, I'd skip the festae and go with the Freddy instead of the jag. Maybe think about the salvini instead of the festae.
I consider the 125/150/180 the same size tank, the 150 being a lil taller and the 180 being a lil wider (which all this lets you do is be able to house a fish that gets a bit bigger). In the end you're still working with a 6' tank and when I see a Festae and a Jag with other fish in this small of a tank it's more or less a ticking time bomb waiting to go off.
Being the owner of a 150 I have the same issue as you do, however instead of trying to force what I want to work, I have asked the advice of others on here as I really really wanted a Festae too.
If you're dead set on having a Festae then dedicate the entire tank to them, it's pretty much an all or nothing type of thing with a 180g. If you want a nice community then you'll want to adjust your stock. I went the second route and really enjoy my cichlids and non-cichlids in the tank.