FYI, I think sajicas are considered to be Amatitlania genus now. Cryptoheros nanoluteus and Honduran Red Points are little beauties that you may want to look at. Amatitlania nigrofasciatum (standard convict) tend be more aggressive, so I'd personally avoid them in a community.
Water chemistry may or may not be that important. Some fish may survive but not necessarily thrive. Other fish may be fine either way. Probably less important if the fish are captive bred and far removed from wild fish.
My personal feeling is that fish should be included with others of the same region, where it is a somewhat believable biotope. I don't think it necessarily has to be a 100% accurate biotope, but combining fish that are obviously SA soft water fish with CA alkaline/hard water fish just doesn't feel right to me. I'd stick with stuff ranging from southern Mexico to Costa Rico if you go the CA community route. And there are lots of awesome CA fish to choose from so that I don't really see the need to add SA fish. If that doesn't matter to you then by all means do what you want.
Here is my CA tank. Started with 15 Thorichthys mixtecos, added some new cichlids recently that I didn't post about yet but will soon, including some sajicas.
http://www.monsterfishkeepers.com/forums/threads/my-125-gallon-central-american-cichlid-tank.673309/
Also check out Darren's tanks, he keeps some awesome CA Thorichthys tanks:
http://www.monsterfishkeepers.com/forums/threads/lots-of-pics-past-and-present.656696/