This is my reply to your previous post (in the beginners forum) where you hadn't listed your plans:
Gouramies are generaly shy fish and don't do well with other large or boisterous fish (such as cichlids).
However, a gourami tank would be a great choice .
For algae eaters, otos are a great option as they are small and peaceful. If you can find them, a SIAMESE algae eater would be even better and flying foxes aren't that bad either but are rather active and I qouldn't realy keep them in a 20 gallon.
There are SO many small shoaling fish to choose from but something peaceful would be best for gouramies - black phantom tetras/black skirt tetras are my favourite tetra and the males display to one another beautifuly. Harlequin rasboras are by far the best schooling fish and swim very tightly packed as well as being attractively colored. Rummynose tetras and golden dwarf barbs are also nice, small shoaling fish.
Danios, IMO, especialy zebras, are stunning fish but are very active and can (sometimes) be too active for a shy gourami tank, causing some gouramies to hide. However, they can also have the effect of reassuring shy gouramies and getting them to come out of hiding. With smaller gouramies, however, I wouldn't suggest them as good tank-mates and with larger gouramies there realy isn't much room that both the gouramies and danios, both being mainly top-dwelling, require.
Good gouramies for a 20 gallon are honey gouramies (colisa chunae/sota) and dwarf gouramies (colisa lalia) and all their variants. Dwarfs look substantialy larger though they are the same size (2 inches) as honeys but they are also much more fragile due to in-breeding. You could keep 2 dwarfs (females are hard to find and less colorful) in your tank with a medium school (8-10) of some sort and 3 otos.
Alternatively, 2 male honeys (not DWARFS) and 4 female honeys (not DWARFS) with a shoal of 7 and 3 otos may also be nice.
Alternatively, you could try a pair of pearls (trichogaster leeri) or a male and 2 females though this is pushing it a bit. Then a shoal of 6 and 2 otos.
A single pearl with a medium shoal and 3 otos would also work. Pearls are stunning fish and the males develop the most beautiful flame-orange and olive coloration. They grow up to 6 inches but are very, very peaceful (except for when breeding or highly territorial males - there are exceptions).
Three-spot gouramies are also a possibility but are more aggressive so I'd go for only one. Opalines are by far the most interesting of the three-spot (trichogaster trichopterus) variaties and both sexes have the same attractive blue coloration.
Moonlight gouramies (trichogaster microlepis) are beautiful fish with a purple tinge in some lighting that is offset by bright orange or yellow feelers. However, though not as aggressive as the three-spot gourami, they grow larger so you could only comfortably keep one and they are best kept in a larger tank.
Other gouramies you could try and are quite common are the croaking (trichopsis vittatus) and sparkling gouramies of which you could keep a similar number as with the honeys. These can be quite fragile.
Also, giant/banded/striped/indian gouramies (colisa fasciata) and thick-lipped gouramies (colisa labiosa) are peacful and moderately sized at 3-5 inches. You could probably keep about 3.
What you must remember with gouramies is that their character can vary and, while some individuals will get along and be laid-back and peaceful, others may take an immediate (or not-so-immediate) dislike to one another and become very aggressive and territorial. However, I think part of the interest in keeping gouramies is derived from their personality and the fact that each one is unique.
Now that I see what you had in mind, rams would work with gouramies and the pleco would too but I don't know what size it would get to. Consider pearls instead of dwarfs and then you wont have room for other fish 
