Guys, I seriously need help for a kitten issue (short term and long term), please!

Warning: This is gonna be a very incredibly detailed question, but I seriously want the best answers I can get for this kitty issue. There’re a lot of things which I need to consider and as I’m a total amateur regarding cats, I need all the help I can get. Please help me Flutherites!

Just today we found a straggly kitten in our shed. For the sake of convenience I’m gonna assume that it’s a male kitten. He’s incredibly thin and dirty. My immediate concern is how to make sure that he doesn’t die. So far he’s been fed some rice and meat and I’ve put it in a small cage. I left the food in there and placed a plate of water. I also arranged a cloth such that it could be used as a sort of mattress. Now, I have a few questions that need answering here.
Question 1: What exactly can I feed this little guy? I called up an animal clinic and they told me that I should be buying him cat food. Okay, if I keep him I just might. But in the short term, exactly what kinds of human foods can I give him? I was told that cow milk is an absolute no-no. Bread was also not advised. So I’m just gonna try to get him to eat steamed rice and fish.
Question 2: Exactly how should I keep him? I feel terrible about keeping him in a small cage (here’s a picture of the cage and him inside it) but I have a shih tzu which has free reign of the house. I don’t want anything bad to happen to the kitten. Furthermore, I’m not sure whether I want to allow the kitten to go around scratching stuff. Another issue is that he’s filthy. I don’t want any of my family exposed to anything potentially harmful. This leads me on to
Question 3: What should I do regarding his physical condition? Here’s a picture of him above the cage. You can see just how thin he is. There are times when I think I see him shivering inside the cage, and if this is the case, what can I do? Furthermore, upon closer inspection of his face (another pic for reference), you can see that it looks quite bad. I’m wondering what those two dark spots at his nostrils are. And can I do something about the stuff at the corner of his eyes? There also seems to be a lot of black dirt within his ears? Can I do anything about that?
Question 4: How should I be attending to him? He’s meowing a lot and very constantly. I don’t know what that even means. But he seems to stop when I get near to the cage. I even hear him purring when I stroke him, but I read that purring doesn’t necessarily mean that a cat is happy. It can even mean that one’s in pain. And should I even move him to another area?
Question 5: Is there any way I can clean him up? He is so filthy. But I have no idea how to go about doing stuff. Heck, I don’t even know how old he is, which leads to the last of the short term questions…
Question 6: Can anyone try to estimate this kitten’s age for me? My domestic helper said that she thinks he’s around 3 months old. But I’d like to get more opinions.

Okay.. Now that we’re done with the short-term things, here’s the long-term issue. My mom is totally against us keeping the kitten. We already have a rabbit and a shih tzu, and she says that she worries that I don’t even have the time for myself to study. But the thing is, I really wanna own this kitty. I wanna raise it and take care of it. But in order to even consider it, I’ll need info on cat-raising.
Question 7: What’s it like to own a cat? Would you say that it’s any more difficult than owning a dog or any other pet? Or is it more fulfilling? Or is that simply purely subjective?
Question 8: How hard is it to train a kitten to not scratch the furniture, or to defecate in one designated area? I can go about looking on the internet about how to do it, but I’d like some personal opinions and tips here if possible.
Question 9: If you have any other pets, how did you manage to introduce your cat to those animals?

And this leads to the last of the long-term questions:
Question 10: I’m not even sure whether I should be undertaking such a task right now. My mocks are in less than three weeks and I’ve yet to really study hard. But is taking care of a pet really going to take that much of my time if I subdivide my time in a disciplined manner (eg 1 hour work followed by 15 minutes of looking after pet, cleaning up after it and whatnot)? Is it necessarily wrong to try to own an animal to also teach oneself discipline as you know that you’re dealing with a living creature?

Thanks in advance for the answers guys. I’d infinitely prefer it if you could give answers for all the questions I’ve asked, but you find that you can’t do that, then I’m still gonna accept them nonetheless. Any answer is better than none!

P.S.
It might help to note that I’ve got to convince my family that I’m capable enough of taking care of the little fella. We’re probably gonna hold a vote today in the house.