Hi
those lists are quite full of contrasts, you kind of have a few choices to make as to if you want a calmer cichlid tank or a bit more of a rough and tough tank. For example the Geos and Threadfin would have a tough time with the stronger cichlids and also would find some of the faster fish in there a bit problematic. Preferably I wouldnt mix these Cichlids with Gourami as well.
The easiest thing is to probably suggest a few stocking lists
But first Ill just run through the cichlids you listed as to how they could work.
Apistos - potentially too small to work with most of the other fish mentioned
Parrot fish - not my personal favorite of fish but could work if this was one of the main requirements
Severum - great fish for this size tank and can work with tons of options
Acarichthys - same as Severum
Geophagus - good candidate for the tank if you have sand, just remember they are gregarious cichlids that appreciate being in groups.
Texas - could work but would be a tougher set up than the geos and sev
Jack dempsey - same as Texas
Pantano - Im not sure even 500 litres are big enough for these truly gentle giant - they get over 2 foot long and are built like a house!
Option 1
1 x Severum (any species or strain, go for a male though preferably)
1 x Acarichthys (stick to one, they can be quite species intolerant)
4 x Geophagus - I would probably go for Geophagus sp Tapajo Red Head as they are a smaller species of Geo and are generally stunning
All Geophagus are gregarious fish and always do best in groups, get them as youngsters and let them form a hierachy as they grow - they will also interact with the Threadfin who will probably end up at the top of the group
1 x Angel Fish - will fit nicely into the tank, how old are they? Im wondering if they could accept a friend/ mate?
1 x Synodontis Eupterus
1x BN Plec
1 x Twig Catfish - what kind of twig is this? Is it a Farlowella or is it a type of Whiptail like Sturisoma?
So that would be the peaceful tank, its quite similar to my tank I have a Severum and a Threadfin
and my tanks 512 liters. I would also still want to add a school of something - some kind of mid sized tetra would work great like Bleeding Heart Tetras or Flame Tetras - or you could look at some headstanders with them, though not Leporinus.
Option 2
1 x Texas
1 x Jack dempsey
1 x Synodontis Eupterus (squeeker)
6 x Silver dollars
15 x Tiger Barbs
1 x Rainbow Shark
Again there are probably more fish for this set up as well. But these are just starting points
If I have missed any of your favorites that you wanted to keep and/or get let me know and we can work up a list that will work for you and the fish
Hope thats helped
Wills