The Glofish you mention, are they the same as the ones in the following link? If yes what type are you getting?
https://www.glofish.com/
Glofish are expensive and to put a dwarf gourami in a tank with them is in my opinion, a waste of money. I know you already have the gourami but they are disease carriers and I totally agree with Byron to try and avoid them. You can't do that because you already have the fish but my main concern is the dwarf gourami and the number and variety of diseases they carry. The two main diseases they have are Tuberculosis (TB) and the Iridovirus. They can have these for months and show no signs at all, then one day they get sick and die. Then all the other fishes in the tank contract it and die further down the track.
If you are buying Glofish, like the ones in the above link, those fishes need to be kept in groups (because they are tetras & danios) and that means you will be spending a lot of money to have a school of them. Keeping a dwarf gourami with them could end up costing you a lot of money if the gourami has TB or the Iridovirus.
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You only need one type of snail. If you have several species, one will usually out compete the other species and you eventually end up with one species. I would keep the mystery/ apple snails because they are bigger, easier to see and don't breed as readily as the livebearing snails that can easily take over a tank.
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Try to make a cave at one end of the tank for the Bolivian ram so it doesn't set up home in the middle and chase the catfish all the time.
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My last concern is about the number of bottom dwellers you have planned for the tank. A 3foot long x 18inch wide tank is good but 12inches high is not. And there are a lot of bottom dwelling fishes that you want.
10 Corydoras and a Bristlenose would be fine, but adding 8 more Otocinclus could cause problems because the b/nose will claim the tank as their own and try to drive the Otocinclus out of the area. Algae eating fishes have territories and defend them quite aggressively. So a 4 inch b/nose will try to chase the small Otocinclus away from its food.
8-10 Corydoras and 4-6 Otocinclus and no bristlenose would be better.