...and the endler's will readily breed with guppies (just a tidbit of info if you didn't know)...
You do
not want to keep Endlers and Guppies together for just that reason. Pure Endlers are hard to find, and if you breed them with Guppies, that perfectly good pure-ness is gone forever. Don't keep them together.
Green Swordtails can be the wild type, but there is also a man-made version which is most likely what you're talking about, sally.

They are pretty hardy fish for Beginners, as long as you have a big enough tank (which you do) and you get the stocking right. 2-3 females per male is the recommended amount, however more then one male Swordtail
can cause some aggression issues. It's ususally recommened to have one per tank, just to rule out aggression, unless you have a pretty big tank.