We had 4 kittens dumped off here at barely 4 weeks, no mama to be found. They did not take to bottles and were on the young side, but I was able to get them on formula mixed with wet food. By 8 weeks it shouldn't be needed and they should be able to do solid food.
They lose their baby teeth right around that time. I bought some teething type toys. They weren't especially interested. They mostly chomped on each other though. Nobody is a biter now at 18 mos and I didn't have to do anything special to teach them not to bite. If you want to do something, I would just gently scruff their neck like mama would and firmly say no while redirecting to petting or something else.
I do not let small kittens sleep in my room until at least 6 mos. Too much attacking of the feet. I don't remember them crying but they also had each other.
My counters are pretty cluttered, not sure I ever had to do anything to teach them not to get up there except put them down, they just don't get on them. They do get on top of dressers, bookshelves and have a cat tree that they mostly ignore.
At 18 months, they don't have any real behavioral issues and are pretty lazy. There is a tiny bit of interpersonal drama between the two boy and each other and also the older males here and there.
Their nails get so sharp when they are babies and it's a good practice to clip them now in case you need to when they are older. I don't trim my older cat's nails much, I just provide things for them to scratch and they take care of it.
It's important that cats have access to hiding spots say if the plumber comes and it is noisy and also they just randomly get spooked by things. Most cats will make their own spots, so unless you have a super minimalist, pristine house you probably won't have to go out of your way for this. They also appreciate cardboard boxes (usually the favorite is one they barely fit in curled up, but you never know which box they will adopt) in different sizes to sit or nap in.
My cats are zoomers
so they like to play games for cats on the iPad and watch videos for cats on YouTube.
Practice shaking the treat bag and calling them so they learn to come when they hear that noise. It can help if you can't find them.