I am VERY new to all of this fish stuff. I had a very ugly betta for a year which lived in a bowl, until it jumped out of its bowl when I was not home and died

. I decided very recently to get a couple
Goldfish, knowing honestly nothing about
Goldfish at all. I originally got these very small
Goldfish and put them in a 5.5 gal tank. Well, I just so happened to be doing a project at school involving fish (the WORST and probably inhumane project my teacher could assign to us) and found out how huge
Goldfish grow.
Well, I bought a 25 gallon tank which is equipped with a 200 gph filter and a hood/light and has two java ferns attached to a piece of driftwood along with a large fake plant. I have one black pop-eyed
Goldfish and one fantail
Goldfish, both about an inch and a half to two inches in length. I have now a bunch of questions and am hoping to get a lot of input.
First, is this set up acceptable? I don't want to get a year or two down the road and realize I really should have bought a 55 gallon tank for these two
Goldfish. Secondly, can I add anything else to the tank? One of my classmates used a pleco for his project, and so far, it appears that it could work okay with my
Goldfish, but I would like a better opinion. According to them, it should only grow to a maximum of 4 or 6 inches but they don't recall off hand the breed (they have a card with the breed on it that they are going to give me next class period). Honestly, I want to save it from its misery because it is currently housed in a cut open 2 L soda bottle with a HUGE plant of some sort in there and more algae than I would tend to believe it could eat in a month. I would love to adopt it to save it from its current what I would think of as torturous state, but if it will kill my
Goldfish, or if my
Goldfish will kill it, I'd rather rescue it to give it to a tropical fish store. And if it would be acceptable with the
Goldfish, how do I get enough algae in my tank to grow? I have those two java ferns, but will that be enough in a 25 gallon tank for plants? I would obviously feed it other things and get more driftwood for it, but I want it to be happy. Plus, how many fish can I keep in this tank? My mom really wants me to get a
Weather Loach because it looks cool, can I get one of those and keep it with my
Goldfish? Would it be okay to get both the loach and the pleco? And finally, what should I be putting in my tank or be doing to it? I put in water conditioner, and I plan on cleaning 25%-33% per week, but should I be testing pH and nitrates and stuff? I have a thermometer on it, but that's it. If anyone can answer ANY of my questions, that would be EXTREMELY appreciated. I am getting very interested in this hobby but I would just love some educated opinions before I proceed. Thank you so much for your answers!