akvamania IF they really are goliaths, which you can't say until you receive them and post pics, then 200$ for a 20 cm is a very good deal. If they are vitattus it's still a decent deal
And ak, trust me, you put those ATFs in the red devils's tank where they've already established territory they'll be picked on relentlessly and probably die. ATFs squabble with each other, but are not bully fish or fighters. They are just pure predators really. They don't tend to fight other fish like wolves, snakeheads, and cichlids. Sometimes they kill fish, but they're not fighty fish.
I would not rist it at all. They need a big tank too, even temporarily DON'T put them in an 80 litre or 125 litre, they'll be nervous and they'll probably damage their snouts as they dart around, and knock their teeth out. They have to go into your 500l until you get your big tank.
I would take the devils out and put them in the 125l, leave the plecos, then when you get your big tank put the devils back in the 500l, and the hydros in the big tank.
Don't keep the hydros with cichlids, at least not until they are over 30 cm. Keep them with peaceful characins and bichirs.
Also have you seen this fish? I don't wanna ruin your trip, but in all likelyhood they are not goliath. Real goliaths are very rare, so many ATFs are marketed as goliath but almost all of them are vittatus or sometimes forskalii. Only 2 or 3 people on here actually have a real goliath.
Here are some pics, not mine.... here is a vittatus, notice the short snout and dotted stripes on the body and the tail...
Now here is a goliath, I'm sure you can see the difference...
As yours are 20 cm, not babies, they'll be very easy to ID.
GOod luck, and they are cool whatever they are.