Hi everyone! I am new here - this is my first post. I am completely overwhelmed with all the internet links I get when I googled my questions, so I am hoping I could get some guidance on how to start my new fish hobby on here..lol.
To sum up a long story, I received a desktop aquarium (2.5L I think) a few months ago as a gift and decided to finally use it. Last week, I bought 2 of the small orange finned goldfish from Petco for it (they were 15 cents each) and hoped they would last a good month until I was able to transplant them to a larger tank. (yes I know, I should have bought the tank first..but..oh well..this is all new to me.

). I bought an API Ammonia Test kit and I was doing the daily water changes because the ammonia levels were super high (on the darkest shade of the strip) and I figured it was because I didn't have a filter in the little tank. I was also putting in a drop of the API Goldfish Protect liquid I had bought from Petco along with the flake food.
Well, no surprise, over the past 2 days, both fish died even though I was doing 50-80% daily water changes and not over-feeding. The first goldfish died on Saturday and as soon as I saw that happened, I did an emergency Stress Coat application on the 2nd fish after changing the water. I panicked when I saw the fish sitting at the bottom of the tank just barely moving, so I went back to Petco and bought a Starter Kit 10 Gallon Tank. The kit comes with its own filter and cover. I also bought a separate water heater and thermometer to monitor temperatore.
When I got home, I filled the tank with tap water, added Water Conditioner and Stress Coat, and slowly added the lone fish into it and rinsed the 10 pieces of gravel from the old aquarium, then added that into the new tank. For first 3 hours, my fish seemed happy, swimming all excitedly in an empty tank with nothing in it. At bedtime, I noticed him sitting sideways in the tank and after reading some messages on here - I decided to add 2 teaspoons
fo salt because I didn't have any peas (I wasnt sure if it was constipated or what..


). The fish remained on its side but I could see it was breathing terribly heavy. This morning I woke up and the fish basically was on its side, and no longer breathing. After 20 min, it didnt even move, took it out of the tank and it was basically a goner.
So now I am sitting with a 10 gallon tank and not sure whether:
(a) I should get another goldfish, or (b) get maybe 5 or 6 glofish instead..??????
I also would like to know:
(1) how do I go about starting a "fishless" cycle so I can make sure the ammonia nitrate/nitrite/ph levels are ok?
(2) is there a general API Test Kit that I can use because all I have are just the Ammonia strips..Do I need to get other types of strips?
(3) how long should I have the water going before adding gravel, decorations and then the fish?
(4) how much more upkeep to golfish require vs. other types of fish (like Bettas, White Mountain Minnows, Ember Tetras?). Is there a web site that actually covers all this info on 1 page?
(5) where is a good place to buy larger fish tanks? I already blew $ 50 for a 10 gallon tank, would have gotten a larger tank but the prices for one ($150 for a 30
gal) just seems so over the top!! How do people afford these large tanks and where do they find the space for them?
Sorry for so many questions but I am a complete newbie to this. Never owned fish before. First attempt at trying to keep my next fish alive!!!

thanks !!