I've seen many bettas in a commune tank, Mine loves the idea of some large schools of Tetras cause from the store I got him from he lived with em. Many people think Bettas wont get along without it being a female of it's own kind. But as long as it doesint have a big fish and is not a creature who hates big tails. Most likly they will get along. But it's mainly personality choices. My aunt tina gave her betta a guppy for fish food, and now it was pregnant and the betta watched over the guppy fry Oo; its one weird pair up but it thinks the fry are his babies and only attacks if he gets attacked first. He's in a good size tank with his adult brood of 60 Guppy males. It's weird looking and you would think they would eat em up. But he would possably attack us if we whent anywhere near em.
I know for examples from other friends of mine who have bettas in big tanks, that it's the personality of the betta that chooses it. So inless it's a fish you really love. I suggest to just go for it =D you never know what your betta will think of a friend intill he's introdused. Most likly though the Sword will godafter it insted of the other way around. A Large tail with a sword will most likly catch the wrong ettention and get the critter inraged. As for the platys you could possably try them, but only if you woulint take it to heart if he ate em as dinner o_o It's personality that makes the betta what it is. And the wild bettas in lagoons live with thousands of other fish for shelter, they really love schools. And if you find the right fishies you could possably get a great community betta =3. Oh and it is also best that if you put a betta with a sertan fish, put a school of them in, that way he wont see just the one. And the other fish will feel safer. Platys especialy =D
I hope that kinda helps. But be careful with the swordies.