Is the GH number ppm (parts per million) or mg/l (milligrams per liter)? I am assuming it is not degrees, as a spread of 0 to 30 in degrees would be everything from very soft to liquid rock. So if ppm or mg/l (which are the same in effect), this is very soft water. A pH at or lower than 7.0 would be expected with very soft water, and the pH will lower due to natural processes in the aquarium. That's fine, just keep it in mind. Soft water fish, but no fish requiring moderately hard or harder water (such as all livebearers). Tetras, rasbora, loaches, most catfish are options as far as parameters are concerned.
As seangee suggested, if you can re-home the lone TB and the lonely loach to the store, even "free," it would help you move forward. The problem with shoaling fish that have been on their own is the probability of increased aggression, sometimes very significant. It is the fish's only way to deal with such stress. Even adding other fish of the same species to the tank now can be deadly. Once fish are impacted by such stress, there is no reversal.
Whatever you do, please do not get any fish until you have thought through the sort of aquarium you want in the end. Tanks with more than one species are termed "community," and many fish species cannot be combined with many other species. There is a lot to consider for a workable community tank. Knowing what you want in the end will determine what you need to do now.
As you have learned, advice from employees of fish stores is hit and miss. Most have no training at all, and as someone who has studied ichthyology in depth for many years, I know there is a lot to all this if we want healthy fish, and that must be our goal.