Those are both valid suggestions. My main question was whether or not I needed to get more swordtails, but the thread brought up concerns I hadn’t thought about.
There is some unclear information in this thread, but I will start with this last post/question. After I say, welcome to TFF.
Your water is not hard enough for livebearers. A GH of 75-150 ppm (mentioned in post #5) is moderately soft (equates to 4 to 8 dGH). This is fine for most any soft water fish species, but it will mean trouble, stress, weakening and eventual early death for all livebearers. Swordtails, mollies, platies, guppies and Endlers are livebearers. Given your source water parameters, you will find it much easier to have success if you select fish suited to your water. There is no "middle ground" anyway, and adjusting parameters means a lot of additional issues along the way.
The initial question asked about swordtails and platies getting along and "shoaling" was mentioned, so allow me to clarify shoaling. Shoaling fish species are those that must be in a group. Minimum numbers are always asked for, and this can vary for some species, but more will always mean healthier and "happier" fish, that is scientific fact. Characins (tetras, hatchetfish, pencilfish, characidium, etc), cyprinids (rasboras, barbs, danios, loaches), many catfish (Corydoras especially), rainbowfish, are shoaling fish. Livebearers are not shoaling. Having a feew of them together is fine, essential for breeding obviously, but not essential as it is with shoaling species.
This brings me to the clown loaches. Loaches are shoaling fish but they are also very social fish and they develop an hierarchy within the group early on. There must be five or more of the species together, from the first; adding fish down the road rarely works, if ever, and this is not fair to the fish. If you will have at minimum a tank that is 6 feet in length--though 8 feet is advised by all reliable sources--you will be OK with a group of five or six or seven. But the group must be together now. If this large a tank is not in the near future, I would return the two clown loaches for their own good. This is not going to end well. I learned a lesson many years ago...never acquire a fish today for which you do not now have the tank that will accomodate it at maturity. Plans change; it is not fair to harm the fish just to suit our intentions.
Loaches and cories cannot be combined in the same tank. I know, some will do this, and claim no problem. But they cannot ask the fish. Loaches are highly social, somewhat aggressive (including during feeding), and territorial. Cories are about as peaceful and opposite as any fish can be. They do not get along together, the cories will always be the losers, and this harms them in ways we cannot see until it is too late.
The Rainbow Shark cannot be combined with cories. As for the loaches, this is hit and miss, depending upon the temperament of both species.
Gouramis are sedate fish and cannot be combined with active fish like danios. The loaches could be issues here too.
I think I've caught the crucial issues, feel free to ask about any of it. We are here to help your fish.