Dear kytz,
If you are serious about fish keeping, may i ask if you are intending to have planted aquarium since this is planted aquarium thread, but of course, we would love to answer anything about fish keeping if we can help.
may I suggest you something, totally tear off your tank first.
1) do you want to have a planted tank? with soil? with holland sand? or just some "easy to take care" type of plants tied to driftwood, or mosses on wood or rocks?
2) then identify what kind of set up you would like to have in your tank? for example, iwagumi, island type setup or what?
3) after identifying your potential setup, gather the necessary to start off, i.e. driftwood, rocks, or any other hardscape.
4) after all hardscape are ready, start putting them into your tank in an organizing way as close to your potential scape as possible.
5) fill water, if you want crystal clear water, do "water-in, water-out" method.
6) run filter, fan 24hrs. lighting, co2 system as per schedule, about 4 hours during the initial week, increase lighting and co2 period for an extra hour subsequently during the next 3 weeks or so, being 7-8 hours the max photoperiod for your tank.
7) let your tank cycle completely first. previous, i think arrow has posted a few links about tank cycling... this is so so so so IMPORTANT!
8) after about 2 weeks, clean up crew may go in to the tank first (Otto, SAE etc...)
9) after about 3 weeks or a month, you may start stocking livestocks already.... (Guppy, tetra, angel fish, or even arowana but definitely not goldfish)
usually, your tank would have been properly cycled for this period, you must have the patience during the initial stage, for you to see a relatively stable tank for near future.
this is why you always see a family happily buy tank,a cheap rm1 anti-chlorine, lights, filter and fish, then come back few days later complaining all fishes died... a classic example is your cute little pearscale gold fish.
explanation for the above is for planted tank setup, but even i do the same for my non planted tank setup.
In my opinion, I dont think there's a need for those test kits, it's a luxury to have of course, but i think the RM100 spend on test kits would have been better spent elsewhere. As for my case, I have never use any test kit before except for the co2 indicator which comes together during my purchase of my co2 system. My tank has a very low death rate of fishes except for those jumped out, maybe due to stress, non stable water condition/parameter or maybe my tank water was too high, about 0.5cm from the tank top.
a food for thought for newbie, pls select nice edged tank, not those curved tank that usually comes with filter/lighting, those lighting is not sufficient most of the time. preferably white colour or almost transparent colour glass glue, black colour are not so nice, IMO. like the one bought buy a forumer for RM25 from xian leng or somewhere.
feel free to ask more question, we would love to help!
just for sharing.
initial setup of my tank.

close to 3 months down the road.

I've just cleaned off my entire aquarium and it's empty now. Yeah, I would love to have a nice planted aquarium, the Iwagumi style of aquascapping is pretty damn nice. I think usually more suited for bigger tanks right? Mine's a 3 gallon only, I did google, and this person came up with a nice setup for it:
1) I might plan to get some tetras or zebra fish for my 3 gallon tank (if I do not plan to upgrade to a bigger one), I hear that fish needs some kind of "hiding" spot to "rest"? Like maybe a under a log of wood, or a fish house of some sort? I'm not sure too, cuz I see the iwagumi concept don't seem to have much hiding spots
2) And also can advise on what type of grass/plants which are easier to grow/maintain? Totally no clue here.
3) For the water in-water out method and also by looking at the pictures you posted, are you referring to an internal filter? I saw that you're using an internal one, with the output connected to a hose and directed further away from the water intake?