So. American Cichlids Suggestions Cont'd

I am going with some So. American Cichlids and have narrowed it down to 3
different species

Gold Severum
Green Severum
Blue Acara
Geophagus

I would like to some input from the group as to if this would be a good
match, i.e. get along reasonably well, offer some variety, need similar
chemistry.

Ideally I would like to end up with a pair of each in addition to a 4" pleco
and a 3" red-tailed shark (if he ends up being a problem with the juveniles,
he goes). Some concerns/questions:

Do I need a dither fish? I have 6 tiger barbs I could use, would they work?

Rather than have 2 of the 4 species be a Severum would there be a better
choice?

Given the potential size, are 4 pairs too much?

Would a Geophagus be happy alone to reduce the total quantity?

I would like to hear the voice of experience, thoughts are appreciated.

About 2-3 weeks ago I posted the message below which gives you the
background information needed.

Thanks in advance,
Steve

I have a 55 gal well established tank the needs repopulating. I have had
angels for many years and they are starting to go (old age I think). I have
standard gravel with a undergravel filter and the pH is consistently between
6.3 and 6.5. Rather than get more angles I was thinking of going with fish
with more of a personality. Non-angel and non-discus Cichlids came to
mind. I don't want to turn the tank upside down by changing the gravel for
crushed coral to get the hard water so African cichlids are out.

Here is my question: What types of So American cichlids would work under
those conditions. Ideally I would like to have 3 varieties that can coexist
given enough structure. I plan on getting them young, how many of each
should I get? Would I need to cull them out for a pair of each type or
would 3 or 4 of a type work?