New 20H - betta, cories, swordtails?

[Hidden Walrus]

Today I picked up a brand new, apparently unused twenty gallon high aquarium, with a Whisper 10 - 15 gallon capacity HOB filter, for ten dollars at a flea market. The tank passed the leak test, and the filter runs fine too - which also doesn't even look like it was ever used.

I found the perfect spot for the tank right under a shaded window, and would like to make it into a low tech riparium, with just a few peace lilies and a syngonium or something similar that will do well in indirect East lighting growing out the top and no true aquatics (tank will be lit only but sunlight and with the background too dark underwater for any real plants I think, maybe java fern or anubias would do alright.) The window doesn't get any direct sun except a sliver in the morning in summer so it shouldn't get too hot. It's also a few feet away from a shop light to the left of the tank but probably not close enough to make a huge difference in lighting for plants.

Obviously I'll have to pick up a heater before I introduce anything, and then there's the cycling process, but eventually my planned stocking (although not planning to start for a while) would be a male betta and 6+ pygmy cories for sure, but I'm not sure what else I could keep with them, if anything. I like swordtails, would really like some for the tank and have kept them before but I don't know whether a twenty high is big enough for a trio in addition to the other fishes. If not swordtails what else would anyone suggest? I'm not a big fan of tetras but then again I've not kept any but black skirts (boring) and neons (which never lived very long for me).
I also was wondering if the 10 - 15 capacity filter would be adequate for the twenty gallon, maybe if it were not fully stocked?

And, if I were to start off slowly, with just the betta in the new tank for example, would just rubbing the cycled filter media in my other 5 gallon betta tank on the new uncycled cartridge, making sure to get some crud on it, and tossing in a few handfuls of the gravel instantly cycle the new tank enough for the one fish? And then gradually I could add the other fish over a few weeks? Or will I have to go about a brand new cycle (I hope not)?

Thank you everyone in advance.

[librarygirl]

It's mostly going to depend on the betta's personality; typically they don't tolerate tank mates and I'd be concerned that the longer fins of swordtails would be very temping for a betta. It could be worse if the betta is introduced first as he'll see the tank as his territory and anything else that comes in afterwards could be seen as a threat.

I'd upgrade filters definitely; an AquaClear 50 should do nicely.

Not sure if just rubbing cycled media in the new filter would cycle it or not; you might do better with a piece of filter pad. Even so it wouldn't be able to hold much, a single betta might be ok, but as you introduce fish the ammonia is likely going to spike. The live plants could help a lot there though but I'd still test and do water changes as needed. Or you could do a fishless cycle with ammonia; that way you can introduce all of the fish at once when the cycle is done and not have to worry about cycling with fish.