The koi angels (or any freshwater angelfish) certainly will act as a curb on livebearer fry. It has been a long time since I have hung out with angelfish breeders, but Google and check around for "koi angelfish and color foods." Some people who raise them have never mentioned this, but I vaguely recall also reading of where the person raising up the koi fry, worked very hard to feed them color foods high in carotenes.

The ultimate coloration of at least one other hobby strain of angelfish (leopard) seems to depend upon a certain level of lighting. Check around for details on those if that raises your curiosity. :)

Also, one of the drawbacks to keeping angelfish is that they will pair off and lay a lot of eggs. Given your faithful water changes, they will grow, pair and spawn. Then, unless you have a 55-gallon tank for each batch of fry (the pairs do fine in 20s), you may need to look for something to cull angelfish fry. ;)

I have fed extra cichlid fry to large killies, but one must feed off those fry very soon after hatching. Otherwise, there is a danger of choking the killie on the rapidly hardening and growing fins. Maybe a large pike livebearer wouldn't mind a break from its diet of rosy reds.

Got a chance to browse Mike Hellweg's new livefoods book put out by TFH. I need to look at it more (and save my mad money). Mike makes a strong point that feeding fry (and a remarkable long list of other creatures) is most appropriate. Hw warns against anthropomorphizing our fish.

I like dwarf gouramis. And it is cool watching the males build their nest. The spawning act is an event all in itself. After the pair has spawned, it is imperative to remove the female soon. The eggs in the nest may be hard to see, especially if we miss the spawning. The fry look like pin heads. (Newly dropped guppy fry are huge in  comparison.) Look for a decided change in the male's behavior and a female hiding as far away from the nest as possible. (In nature she would flee away from harm by stealing down the shore or across the pond or rice paddy. That allows females to forage for food and rebuild her egg supply. while the male watches the nest. When the fry are free swimming, though males may leave them alone for a while, there no need to keep him in there.)

Is the platinum dwarf gourami another commercial sport of Colisa lalia? As you know, there is the even smaller honey gourami a.k.a. the honey dwarf gourami and the red flame honey gourami.

By the way, I doubled checked names at the quite authoritative Fish Base http://www.fishbase.org/ComNames/CommonNameSearchList.php
and was very surprised to see that the honey gourami is now Trichogaster chuna (previously   Colisa chuna or Colisa sota). The dwarf gouramis are still being called C. lalia, though miss-spellings of that name are common on the Net.

You may need some very small food for the fry. To get a good sized batch raised up, you probably want to hatch baby brine shrimp. I would suggest hatching two modestly sized batches, starting them in alternate days and harvesting alternately. The empty culture should then be restarted. The salt water should be replaced if it seems at all rich organically. If there are extra bbs (baby brine shrimp) there are certainly livebearers in the Beast who will take care of them.

Some gourami fry will grow up in a well planted tank where they can take some microscopic food items growing on plant leaves. A greenwater pond without predators might serve them sell. The plants or greenwater should be supplemented by some small dry food and clean up corps of pond snails. Mosquito eggs rafts hatching and micro Daphnia (such as Moina) are welcomed too.

Enjoying pretty warm water (75-84 F/24-29C), the dwarf gourami is one of those "lazy, hazy, crazy, days of summer" spawners. Certainly they will spawn at other times in heated aquariums, but a dwarf gourami nest goes well with long sunny days, ball games on the radio (while doing things in the fishroom), the softball and little league games in the park, visiting friends, meeting half the neighborhood (while being taken for walks by the schnoodle), puttering around the yard and feeding 20-gallon container "ponds."

Re-roofing, painting and falling off of ladders will never make the hit parade. ;)

Your big aquarium is great for raising larger swordtails. We too often either crowd them or keep them in aquariums smaller than ideal.