If you're doing an Amazon themed tank, try and stick with SA Cichlids. There's no reason why you have to but the half-biotope style tank with same continent Cichlids is something I like, especially considering full biotopes are limited heavily by what's available in your area, especially to me in Australia anyway.
4x2 isn't a big footprint, a male Carpinte isn't going to go down too well in it if you want a fairly peaceful community. If you like keeping fish in multiple numbers, which your last post suggests, and you like big 'showy' fish, which your pick of Brasiliensis also suggestions, perhaps try something like this.
2x Heros sp. 'red shoulders' (Rotkiel)
3x Uaru amphiacanthoides
3x Geophagus steindachneri
Now what Geophagus you pick comes heavily down to personal preference. Look around heavily for photos online of these guys before you make a choice, or try and find some in person, because it's very rare that photos do them justice. My suggestions are also for Geophagus that max out at around the 5-7" mark, 125 isn't an enormous tank, so other possibilities include Geophagus sp. 'Tapajos Orange Head', Gymnogeophagus balzanii, possibly Acarichthys heckelii; have a browse around.
In case you don't like Uaru.
3x Heros sp. 'red shoulders' (Rotkiel)
2x Hoplarchus psittacus
3x Geophagus sp. 'Pindare'
All of my suggestions go hand in hand with none of these fish being breeding pairs. 4x2x2 is not a big enough environment for breeding cichlids to co-exist inside.
it just is not possible 
