Depends on the dimensions more than anything for the gibby. A 125g would be no good if it was only 1ft wide, but if it were 2ft it'd be ok. 18" would do for a smaller specimen, but once they hit 12"+ it'd be pushing it - they're chunky plecs that have a hard time turning, my 15" one couldn't turn in an 18" wide (135g) tank so we had to rehome him. As they can get to 18-24" (although 18" is the norm), I wouldn't go for anything smaller than a 2ft wide for a permanent home
As for the cichlid inhabitants stocking level, I think you'd be pushing it with 5 festivums. Maybe one or two, but 5 would be really pushing the amount of territory each fish would have with all those others in there. And keyholes might be a bit small - although if you were adamant about getting keyholes, I'd pick a group of them (maybe doing without the festivums), as they prefer to be in groups and are smaller.
What are the dimensions of the tank? I'd probably go for:
Green Severum (one)
Firemouth (one)
Keyhole Cichlid (three)
or two female convicts
Festivus (two)
Salvin's Cichlid (one)
I'm not sure about the salvini as I've never kept them (and I think they're quite feisty if I remember rightly?), and from personal experience, the festivums aren't as peaceful as they're made out to be (mine killed and/or maimed several fish in my tank - including some very expensive and well armoured plecs) - so the quieter keyholes might not be the best choice? A couple of female convicts instead would be ok
I took the blue acara off the list as I hear they're quite boisterous too, but if you got convicts instead of keyholes, you might get away with it.
But really, stocking advice for cichlid tanks isn't really the be all and end all. All cichlids are different - you could end up with a scaredy cat firemouth, or an arsey severum, and it'd throw your whole plan out. Only way to find out for sure is to try it - and have a spare tank and/or divider handy