oh, from my knowledge they got 6-8 inches, I don't know about the julies though, getting a few of each seems fine, I wouldn't say the tank is overly small and I don't think those kind of cichlids are overly aggressive, I was just thinking 2 of the marlieri, regani, marksmithi, dickfeldi cichlids, with how rocky the environment is I think it would be ok, I don't see why it wouldn't work, it's only 8 small cichlids and I understand you aren't trying to be mean, I only have a 29 gallon so this is what I'm limited to, Ideally I'd have a 90-120 but this is all I've got"Aztec carpintis cichlid" im assuming you mean hericthys carpintis- they get to about 12" long, beefy, and highly aggressive. Definitely a bad idea for this tank.
This is a very small tank, I think you will have much better luck if you tone back your stocking ideas quite a bit. I don't want to seem like a negative guy or rain on your parade or anything. But if you try any of these ideas you have- large predators, large cichlids, mixing many cichlids- none of that is going to work beyond the very short term in a 29 gallon tank.
I agree that one juli species would be much better, get a group of one species rather than a couple of each, that way the aggression in the group is distributed evenly and you can watch the group behavior. You could also add some shell dwellers with the juli's such as N. Brevis.