That is 37 fish; you might be able to pull that off in a 40 gallon especially since you'd be getting rid of the clown loaches, but a 55 would be better. There is no way that those fish would fit in a 20. For reference, I currently have 12 fish in my 20 gallon tank. Keep in mind that a 20, while not "tiny", IS on the small side of the tank scale. Also remember that if you're looking at the fact cards on the tanks at, say, Petsmart, the sizes that the fish reach are generally grossly understated to get people to buy them.
I'll go down the list here:
You can probably forget about the glass catfish; those will likely get too big for a 20. A couple may be fine, but they like to be in bigger groups and thus would need more space.
If you heavily plant your tank or manage to get one male and one female, the dwarf gourami would be fine. If not, I'd stick with one as the males may fight one another.
Pearl gouramis get too large for a 20, so those will have to go too.
That number of glassfish would be fine, depending on what else is in there. Ditto with the rasboras, the x-rays, and the hatchetfish.
A group of 5 bloodfin tetras would be better as they like to school, but not with all of the above fish.
A Tatia Perugiae would be a great choice as a small bottom feeder, though make sure it has a cave to hide in as they are nocturnal. If you have one of these, you should probably skip the cories.
I'd leave the clown loaches alone. They get far too large, though I suppose you could have them temporarily if you are giving them away. (I assume that is what you mean, since I'm thinking you don't already have a larger tank or any tank if you're confused about stocking.)
The Panda corydoras (or any corydora) I have always heard provide larger groups. However, I hear the same things about otocinclus and my pair are perfectly content without any other companions. These are also bottom feeders, so I would recommend choosing between them and the Tatia Perugiae. Remember that they will probably need special sinking bottom feeder pellets in addition to just cleaning up.
Don't bother with the Chinese Algae Eater. Not only do they get much too large for a 20, but as they get older they lose the taste for algae and develop a taste for the slime coat of your other fish. They will start "attacking" them to try and eat this, and end up killing them. Not a good fish to keep with other fish.
That said, here are some stocking plans to consider that are still on the heavier side (meaning that you need to do religious biweekly 25% water changes):
Varied Tank:
1 Dwarf Gourami (Centerpiece fish)
4 Glassfish
4 Hatchetfish (assorted)
4 X-Ray Tetra
1 Tatia Perugiae OR 2 Corydoras
2 Otocinclus (unless you want to scrape algae yourself)
Total: 16 or 17
Tetra Tank:
5-6 Glass Bloodfin Tetra
6 X-Ray Tetra
1 Tatia Perugiae OR 2 Corydoras
2 Otocinclus
Room for centerpiece fish OR a few more tetra
Total: 16 or so
Very Heavily Stocked:
1 Dwarf Gourami
4 Hatchetfish (assorted)
4 Glass Bloodfin Tetra
3 X-Ray Tetra
4 Glassfish
1 Tatia Perugiae OR 2 Corydoras
2 Otocinclus
Total: 19 or 20
You don't want to do any more than that unless you're working with something small like guppies or neon tetra. Keep in mind that you must cycle your tank first, and add fish gradually. If you add all of them at once in a new tank, many of them will die. You can fishless cycle, but most people start with a couple of the hardiest fish that they plan to keep to get things moving. Then they add a few others two weeks later, then a couple more in another few weeks, etc. The best way to cycle a new tank is to get the filter media (cartridge) from an existing tank and let it float in there with one or two fish to get things moving. It contains an entire colony of the beneficial bacteria needed, so it cuts the usual cycling time (4-6 weeks) way down.
I hope this helped! I know it's exciting to plan on stocking a first tank and you tend to want to put as much as possible in there, but it won't be fun if you overstock the heck out of it and then everything dies. So, be patient and keep the numbers reasonable, and you will be much happier with your tank! :)