im setting up a new high tech tank, what centerpiece fish should I choose

[2tank]

The Geophagines are out, because they are eartheaters. You can't keep Acarichthys, Geophagus, or Satanoperca in a carpet tank. You're also going to have a hard time with a centrepiece if you design the tank like the photo. It's a completely bottom oriented design. Any large fish that rises to the surface area will also shut down its colours because it would be exposed to predation.
The tank also has no centre. The moss rises in the middle (beautifully), and with the exception of hatchetfish or tiny rocket kilies (E annulatus), most fish will want to stay below the highest point of growth. You have this shape ^. A centre needs this shape V. There's nowhere for the 'piece' to fit.
Some Rainbows - trifasciata, boesemani, sexlineata, http://rainbowfish.angfaqld.org.au/Melano.htm as you'll see on this excellent site can blow ugly little discus out of the water, as can cardinal tetras in huge groups and a lot of killifish. Don't even look at linebred Discus, as over-rated, sickly beasts (okay, I'm being a troublemaker).
We automatically think larger species when we get larger tanks, but my nicest large taank had a tetra community with 50 cardinals in it, along with some large wild caught angels. I had to rehome the fish as I'm moving, but I'm going to do it again when I'm settled, minus the angels.

maybe I should do some cherry barbs, or like you said some tetras

 

[Lajos_Detari]

maybe I should do some cherry barbs, or like you said some tetras

Yes, since you have soft water, you can consider Tetras, Rasboras, some Barbs or Danios.

Usually the strategy is to fill your tank with 1-2 big groups of schooling fish.
And get a few bigger individual fish like the Dwarf Cichlids, Pearl Gouramis, etc.

Some Tetras are small and slim but have striking colours like the Cardinal Tetras and are great schooling fish.
Red Phantom Tetras, Bleeding Heart Tetras, Rosy Tetras are not bad and peaceful.

The bigger Tetras are like Congo Tetras, Colombian Tetras, etc but slightly more aggressive.(can be fins nipping).

Most Rasboras are small and more common types are Harlequin Rasboras, Espei Rasboras, etc.

Bigger Barbs are like the Denison Barbs (Red Line Torpedo Barbs).

For Dwarf Cichlids, some species are like Blue Rams(German Blue Rams) Electric Blue Rams and Golden Rams but require warmer water. These are all bottom level fish.

Other Dwarf Cichlids are like Apistogrammas Cacatuoides, Agassizii, Bitaeniata, Trifasciata, Panduro, etc are also bottom level fish.

You can also consider Pearl Gouramis. Get a few of them to have more impact on your tank.

 

[Lajos_Detari]

Some videos for you.

https://youtu.be/AKNR9gGlSD0

https://youtu.be/mfyxhyJaeSA

 

[itiwhetu]

Please show us your tank as it is now, then we can help you

 

[Colin_T]

Rhadinocentrus ornatus (either a red or blue form).

 

[2tank]

the scape is coming along nicely just waiting for my bxyla japonica to arrive, and the rest of the hair grass.
I had an out break of diatoms over the weekend and they covered most of the hairgrass, ive done my best to clean them off.

@itiwhetu see pics above

 

[2tank]

it is nowhere near ready for fish.