VERY happy to hear that you're willing to return the poor little guy and give him a chance to live a happier life in another tank!
It's hard and sad to send away fish that you really love. I had to do it too when I first started, so I understand. But the plus side is watching the fish you DO keep live long and happy lives! When you get fish that are going to thrive in your water/temp/tank-size, and in the numbers that will make them feel secure, you'll be rewarded with a tankful of very happy creatures that can live to their full potential - and that's all that any of us want :)
Well, Swords are adaptable, so they'll likely be okay in any conditions, as long as the water is kept clean. You may want to increase their numbers - but first you really have to decide on which fish you really want to keep, as you can't increase the numbers of EVERY fish you have - if you did you'll be seriously overstocked. Giving the Loach a new home is a great first move, but you now need to figure out where to go from here. I'd say that the Swordtails are a great option for keeping in this tank, because they're a great fish for a beginner, are bright and colorful, and NOT bottom-dwellers like many of the rest of your creatures!
HOWEVER, I'm not sure how the Dwarf Gourami interacts with Swordtails, so you may want to check on compatibility issues here. . . from what I've read, it is possible that the bright colors of a fish like the Sword can make the gourami be more territorial and aggressive, as he feels like he's in competition with them. I could be wrong, but you should definitely do a bit more research on keeping these two together. I think that a calmer shoaling fish is generally considered best in community with DG - like a small tetra or rasbora.
As far as getting another. Honestly, the Dwarf Gourami is a BEAUTIFUL fish, but they do tend to be on the snippy side in a community. That, paired with the fact that they VERY commonly come in with illnesses that might not be obvious until a few months down the road makes me want to tell you that if you want to keep a DG, only keep one. A better option for you would be to return the dwarves, and go with another type of NOT dwarf gourami - like the Honey - who are much sweeter fish, and more tolerant in general - just all around better community fish. If you want to try for a 2nd, a female is the only option - two males will not get along. Even when keeping a pair, you will have to keep a continuous eye on things and have a back-up plan in case they need to be separated - sometimes the male dwarfs can be too aggressive - even to their own mates!
If you DO get another Dwarf Gourami, you should really keep it in QT for a period of 6-8 weeks, because they are so commonly ill. . .