Personally, I've not had any success trying to keep all sorts of severums together in my 90G and 150G tanks. THe only thing that has worked for me has been a M/F pair that have decided that they like each other, or a solitary severum per tank.
I'm sure that if you stick a load of severums in a 125G they will not kill each other, nor will they actually be happy.
For a 125G, I would be looking at a lone sev, a pair (or a lone ... they can also be argumentative buggers) angel. Maybe a pair (or lone) acara or port cichlid.
For geos, I'd be looking at the Satanoperca genus, as you will be looking for a singleton or a pair. True Geophagus genus species generally don't do well in small numbers. Satanoperca species can work if you have a singleton or a M/F pair.
Fill up the numbers with large tetras (bleeding hearts are perfect !) or rainbows (yes, I know they are not SA).
Have fun setting it up ! Remember that cichlids are basically argumentative, territorial fish. Trying to put too many in small space just doesn't work.