the bumblebee gobies (particularly the one on the left of the last picture) have stress colouration - you see how he's very faded compared to the other? They do this when stressed (literally anything from the stress of being netted/bagged up, transport to your tank, settling in, temperature change or poor water quality - they are a very good indicator fish!) and it gives you an indication of who to keep an eye on. The Gobies are less likely to tolerate poor water conditions than the rest. That being said, from the pics you've put up, no one looks too bad or too effected by the water conditions just yet, other than the Goby - so that's a good thing.
From what I can see of your test strip results your KH is 0, your GH is a little above 0 (maybe around 10), nitrite 0 and Ph 6.0. Is your Ph really 6.0? That's quite low for most of the fish you've got. Do you guys in Aus have naturally soft acidic water? I notice on the website you provided they have lots of buffering products. Guppies tend to prefer something around neutral or higher, but they do adjust. As far as the Gobies, they actually swim between strong brackish and freshwater, so they tend to prefer much harder water with a higher Ph (salt in the water raises GH, KH and Ph) so how they're going to do long term in your setup I'm not sure. The Gobies once settled are very active and will use all of the tank, they will stick to the glass high up, low, everywhere. Once they are settled is when the nippy/territorial behaviour comes out. For the sake of your guppies and the gobies preferring different water conditions I honestly recommend taking them back but that is up to you. If you want to keep them, you'll need to break up line of sight a little more with plants and décor. Bare in mind if they start nipping over the next few weeks while your tank is still cycling, this will open your guppies fins up to bacterial infections and finrot etc due to the unstable water conditions so do keep a good eye on them as you don't want more problems than you'll already have!
I've had a look at the site you linked to, and the only thing I can see that store carries is Seachem Stability, which I believe you already have? It's a bit limited choice! I've had a look at the product and it says there's no danger of overuse (didn't think there would be) so if it were me, I'd be overdosing this product for the first week. It says to dose 1 capful to 40 litres on the first day, then one capful per 80 litres for 7 days. I'd test your ammonia today, dose 3 capfuls and test your ammonia tomorrow. If the ammonia has come down some tomorrow, dose a couple of capfuls a day for 2/3 days, then if it continues to come down and you see a reading of nitrite, do the capful for the rest of the time until results are normal.
If you have a cycled filter running on another tank, you can just take a bit of the media out of that filter (a bit of sponge or whatever) and squish it into this tanks filter to seed it, and that will help a lot. If you don't, give the store a ring and ask if you can purchase a small amount of their mature media on their tanks. This really will help immensely. As far as the filters turnover, it's not going to help whatsoever in the cycling process no, only good bacteria can do that and the problem is you have none.
I'm not too up on gourami's in truth, so perhaps someone can help a little better here but I'm thinking 3 in a 2 foot tank may be a problem? Hopefully someone can confirm/correct.
I hope all this helps!