Here's my info vomit. Feel free to ask any specific questions.

Obscure health advice:

If your cat starts regurgitating kibble that appears largely undigested, chances are they are eating their kibble too fast which made them throw up. It doesn't warrant a vet visit, just make it so they eat slower by giving them a slow feeder bowl or smaller portions more frequently. Drinking water right after the kibble can exacerbate this reaction.

Food and eating:

Kibble sucks, but it's cheap. Cats are better off with wet food and it's good to mix some extra water in. They get most of their water from eating. It's healthier for female cats, but necessary for male cats as they are likely to get life-threatening urinary tract infections without enough water intake.

If you still want to feed with kibble, try to still give your cat some wet food each day. Good water intake and not over-feeding kibble = good kidney health. Many people who only feed kibble end up giving their cats kidney disease.

Behavior:

Cats are curious, they have the mindset of a toddler. Most bad behavior is due to one of their needs not being met (boredom, lack of vertical spaces, tepid water) or the human misinterpreting the cats communication. Discipline will only make them afraid and untrusting of you. Cats also express boundaries and understand consent in ways that most dogs don't.

Bites and scratches are usually from crossing boundaries. Trust is earned, which means respecting those boundaries. Learn how cats communicate with their eyes, tails, and other body language. Once you do this, you will unlock a deeper relationship with your cat.

Cats need 15 or so minutes of intense play a couple times a day. Having multiple cats helps with this, but isn't a replacement for dedicated play. Cats also thrive with a regular, reliable schedule. If you find your cat scratching where you don't want them to, provide a scratching post nearby.

Cats are both predators and prey, most people only think about the predator part. They get nervous of potential threats and one of the best ways to help them be happy and confident in your home is to provide them with spaces to hide and vertical spaces where they can observe the majority of the room. Windows facing trees/wildlife are a great spot for perches too.

Show them respect and love and they will return it in kind. Some bites are warnings, some are love bites. If a bit or scratch draws blood, chances are you did something wrong. Don't play with them using your hands or you'll train them to attack your hands and feet. Use a feather wand or comb or something.

Resources:

Cats.com (formerly allaboutcats.com, website and YouTube)

Jackson Galaxy (website and YouTube)

Both will lead to advertisements for products, but both are very knowledgeable and back this up with science. Cats.com does good research on food in particular.

Outside time:

The quickest way to shorten your cats lifespan is to give them free roam outside. There's no reason to keep them cooped up indoors all the time, outside enriches their life as much as yours. Make outside time supervised. Use a harness (not a collar). I've known people who have trained their cats to go on hikes and ride in a bike basket, there's no real limitation to the adventures, you just need to work up to them slowly. Some cats are extremely anxious and may never be ready due to trauma they experienced as a kitten.

Safety:

Check if your house plants are toxic. Your cat WILL at least nibble them (mine kill anything in reach). If it's mildly toxic/an irritant, you can probably hang it out of reach, if it's deadly to ingest, you should give the plant away.

Recommended products / relatively cheap and healthy foods:

Kibble: Wellness complete heath grain-free, chicken

Wet food: BFF (by Weruva), try out different recipes and find what your cat likes. It gives one of mine terrible farts, but she won't eat alternatives that don't lead to stinky farts.

Clay litter: the best I've found if BoxiePro clumping litter

Wood pellet litter: the big bags of pellets they sell for horses at ranch supply stores. Far better for the environment, generally will not work in an automatic litter box.

Best quality of life purchase: it's ridiculously expensive ($200-500?), so I feel like I shouldn't even mention it, but the Litter Robot made taking care of my cats and leaving town much easier. Get the 3 or 4, the functions are essentially the same. I think you can do a trial period if you don't want to pull the trigger. I wouldn't normally recommend something so expensive, but it seriously improved QoL for me and was worth it.

If your cat doesn't respond to catnip, try catnip with silvervine. It can be found for really cheap. I get smartykat brand, but it's no different from other brands or homegrown plants.

I got my cat an automatic feeder thing for like 50 euro. It gives portions throughout the day and prevents her from over eating. The portions are weighed even so that she never eats too much.

The advice I can give is you have to let the cat choose you. I'm sure you can get any cat to like you, but my cat chose me and we've been inseparable ever since. He's sleeping by my legs under the bed sheet as I type this.

Also, put some money aside just for cat related things like visits to the vet and stuff. That shit be expensive sometimes.