Heysus Christos, big question! I'll take a shot.

The larger the tank the easier. Counterintuitive, but consider balancing the chemicals in a 1G tank vs 50G. Ya got a little leeway in the 50G, tight specs in the 1G. Go as big as you can, less care needed.

Start with a thick substrate. I like pea gravel from Lowe's. Big bag, stupid cheap, nice colors, rinse only what ya need, easy. You can buy aquarium gravel from the store, but gravel's a buck a pound vs. $5 for 40#, looks natural too. Also, the aquarium gravel paint chips off over time, looks like crap. Whatever you do, go for a dull, natural, dark color. I went neon one time and my fish looked like swimming turds in contrast.

You want the substrate thick, 3" at least, preferably 5" if ya got a big tank. Bacteria post up in there and help balance the water. Poop works it way in, gets eaten, turns to nitrates (😁) instead of nitrites (☠️). More on bacteria and testing later. You need bacteria.

You need a pump that moves water. Circulating keeps the water exposed to the surface because gas exchange. Seen those bubble stones people use? Oxygen doesn't come out the bubbles, it comes from the bubbles disrupting the surface. Mo surface area on top of the tank, mo mixing, mo better. Get a regular tank as a beginner, not a tall skinny one with little surface area on top.

That pump is also your filter. People fuck with it too much. Let it roll. Those helpful bacteria build up in the filter media. I like these filter stones. They have tiny holes to house the bacteria. Anyway, they sure don't hurt, just don't wash 'em!

Only other hardware is a siphon. (There're other goodies, we're sticking to essentials.) You'll need that to change some water every month or three. If it's a healthy tank ya only need pull 10% of the water, no more. Don't go nuts on this even if the water is cloudy at first!

Another tip on water: Rainwater if you can collect it is best. Otherwise, it's like house plant water: Fill a bucket or whatever with tap water and let it sit a day, preferably in the sun, to release the chemicals. No, this isn't some anti-vaxxer cHemICaL rant, but they put shit in there to keep things like algae down. We don't want that. Done this for 30-years, trust me on this part.

Got all the gear? Fill your tank will cold tap water, whatever decorations ya want, drop a few drops of bleach in there, fire up the pump, wait a month. (Please wait at least 2-weeks.) The helpful bacteria that break fish pee (nitrites) into mostly harmless nitrates will show up and get to work. Sometimes I'll drop a Mystery Snail in right off. They're tough enough and get the pee-to-nitrate cycle jump started, but I've still killed a couple going too fast. No go fast.

If you're worried about the aforementioned nitrites/nitrates, get some cheapo test strips. They also measure ammonia (fish pee). Not really needed if you take your time with all this. Nice learning aid, but don't freak out over results that are a bit off!

Buy all this crap off FB Marketplace or Craigslist or the thrift! You will get robbed at Pet Store™.

We're not ready to talk animals yet, but this basic setup that doesn't take much attention. Tanks are like swimming pools, gardens and house plants: Beginners feed 'em and fuck with 'em too much. Take your time and let it ride.

Questions? I got WAY more details, like a lid and lighting, but ya gotta start from the beginning. :)

The secret to an easy aquarium is live plants imo.

I'd start with 15 gallons personally, but you can go higher since more water means it's more stable. More water does mean harder water changes.

I usually try and aim for a more natural aquarium, I usually fill mesh bags with dirt and then pour sand over it (I like black sand). I aim for 2 inchs in the front, three in the back of more (a gentle slope is really important lookwise).

If you pick easy plants, you won't need much lighting, I have one bulb from above angled and a cheap Amazon led light directly above it. Look up the plants online and aim for something that doesn't need CO2 or intense lighting. In my current one I have: Christmas moss, dwarf sword grass, polysperma rosanervig and water sprite.

I basically plant and then add water, I wait a week or two, then add snails (super important, just get bladder snails, your local fish place will probably be okay with giving them to you, they are technically pest snails but they do good cleaning up). A week or two later if my parameters are good, I add a few shrimp. Then after a month or two aonce the shrimp have bred and their young are a good size, I add fish.

For fish it really depends on what you want, you will have to look online. I only get nano fish really since the bigger ones will eat adult shrimp (eating shrimp babies is fine tho). Shrimp are super cool and keep the tank clean for you so they are a must in my tanks. Fish are added last. Some fish like pygmy corys can be clean up crew as well.

Never ever get live breeding pairs of fish or live breeding females (guppies, platies, etc). They over breed and out compete everything in the tank, females give birth months after their last breeding. Males are fine though, and guppies cannot be killed tbh.

I also like to add a purple mystery snail, there's a lot of really cool snails, as well as an amano shrimp sometimes. African dwarf frogs can be cool too, but are rough on plants. There's more than just fish. Depends on the size of the tank and all. Some fish jump out more than others.

I have a simple sponge filter but tank kits usually come with a hang on back filter. I like the little magnet sponge to make cleaning the glass easier. My lights are on timers and I have an auto feeder that lasts a month. I change about a bucket of water every month, as well as prune the plants. If you want, get an autofeeder with little compartments, not the one that has a screwing motion. Also an air stone and compressor are also a must.

I'd get a plecostimus, you'll want a tank, heater, water pump/aerator (especially if you get a deep-ish tank), gravel, bucket and some plastic tubing (the last 2 for gravel cleaning/water cycling)

You should let your water mellow and do some chemical tests on it before adding fish to it, you might want to start with some throw away fish or particularly hardy fish.

Don't over populate your aquarium, don't rush too many fish into it too quickly.

Another decent option is a beta fish in a planter aquarium, you won't need to do barley any maintenance with that. They love hanging out in the roots of plants