The tank will not be cycled in 6 days (the 25th) you need to cycle it first. No more than 1 goldfish or 2 guppies.
The thermometer... is it a stick on the side one? Throw it away, get the glass one that bobs around in the water... much more accurate.
My favorite fresh water aquarium water dechlor is NovAqua. It keeps your PH good and has stress coat in it, too.
Do you have the filter media? The stuff that goes inside the filter?
Do you plan to use any extra air bubbles? Like the cool ornaments that open up and let air out or even just an air stone? If so then you need air line tubing, the air stone and an air pump. They do oxygenate your tank so they have a use in addition to being pretty :)
Where are you going to set the tank up? Do you need a stand or do you have a sturdy table?
A lighted hood... some fish like to jump out, plus a tight hood will help with water evaporation in the dry winter months. It also helps to keep grubby hands out of your tank (and I don't necessarily mean children) only the person who cares for the tank should have their hands/ arm in that water, and only clean hands!
A test kit is nice, when everything goes to zeros, you will know your tank is cycled and can add more fish... 1 or 2 at a time, wait a week, let your levels get back to zero before adding more fish! You can kill them all if you dump a bunch of fish in there.
Good luck! Go slow and you will be fine!!!
A tank running with no fish or no bacteria will not get any bacteria unless you put some in there, a fish, a dirty filter from a tank that you KNOW is healthy, there are chemicals/ bacteria in a bottle, but I have never used that stuff. Be careful!!
Keeper of fish for 40 years
I have a 55 gallon guppy tank, 75 gallon salt water, 10 gallon guppy and 20 gallon betta tank all set up in my home.