(1) At what size can I expect these fish to begin breeding ? I'm assuming that if they are showing dimorphic characteristics (color), that they should be ready to start at any time now.
I think they are probably sexually mature at 12 - 14 months old. Color is also a dominance issue, and so having a male pop his colors shows he is the boss. While it can be easy to tell the males, it is always the females that are harder to ID since males will hold the female coloration to avoid confrontation.
2) I've read that Venustus males are intolerant of other Venustus males in the same tank. Is this true ? If I can Identify more than one male, should I start to split the group up into smaller colonies trying to maintain a decent M-F ratio ???
I would keep an eye on them, but I think your tank is large enough, and hopefully long enough that it will be able to support multiple males. In larger groups you don't have to concentrate on ratio's, multiple males will take a lot of aggression away from the females. And that is a good thing. Subdominate males are often observed spawning also. If someone is getting totally trashed, then get them out, but generally in groups that have been raised up together they will tolerate each other better.
(3) Diet..... I've read that they're vegetarian, and I've also read that they're omnivores. Can anyone speak from experience with regards to diet ?[/color]
N. venustus is an ambush predator. He prefers to pick off his victims on the sand. So they need a good cichlid staple food, that provides a well balanced diet. They do quite well on most of the cichlid pellets that are available.[/color]
(4) Interbreeding. Should I be concerned about the possibility (if one exists) of the Venustus crossbreeding with the Linii ?[/color]
Yes it is very possible that they could cross. Remember any mouthbrooder can cross with another. and in this case it is the females that pick the male. Everyone loves a big blue male!
Hope this helps you, sounds like a nice group in the making!