Hi Tylerlott and Welcome to TFF!
It's great that you are getting a start on thinking about your future stocking. It can take quite a while to put it all together! Glad the other members have already mentioned that goldfish are coldwater (and really pond animals mostly) and don't work with tropical (tropical means a certain temperature range) fish (goldfish also need vast amounts of water!)
Unfortunately, your first lists of fish hint that you haven't had a chance to think about which fish like water that is harder (has more mineral content) and which perfer softer water. Sometimes information about local water hardness is well known, but it is even better to actually talk with your water authorities to be sure and better still to actually measure the various components of hardness (GH and KH.)
Many tetras (particularly neons for instance) are fish that come from and prefer softer, more acid water. Mollies, on the other hand, are at the opposite extreme and like water that has lots and lots of mineral content. It's not to say that community tanks don't sometimes have success with mixes of these common fish but it's the kind of detail you can learn here and then tailor your stocking plans over the next weeks while your biofilter is building up as you fishless cycle.
Another common livebearer (mollies are livebearers) that likes hard water is the guppy. It's a fish that sometimes has trouble in new tanks if there are still traces of ammonia or nitrite from the filter not being quite ready and does much worse with this if the it's water happens to be soft and acid. Platties and swordfish are livebearers that are somewhat more hardy than guppies in general and not so needy of hard water like mollies. All livebearers however can be somewhat difficult for beginners because they have so many offspring so quickly. This causes the bioload (amount of toxins being created by the fish) to fluctuate more quickly and be a challange to the filter. So babies can be exciting but can be a lot of extra work, what else is new, lol.
Tetras come in many, many varieties and do not produce offspring so readily but they often need to be in groups of 6 or more at a minimum, so planning for them involves knowing about that. Gouramis come in different sizes (which is important) and can have different personalities and need numerical stocking based sometimes on which particular gourami they are. Cories (bottom dwellers) are also fish that need to be and are wonderful when kept in larger groups.
Let us know when your adventure finding out about the local hardness picture has some new information to report! Oh, and by the way, they'll be a number of recommended supplies if you haven't already got them, such as a good liquid-reagent based test kit and a gravel-cleaning siphon and thermometer!
~~waterdrop~~
Thanks for your help again. Do gouramis prefer softer or harder water?
