Two Questions

For question #2, I have a little experience, but there are some great websites about introducing cats out there, too, just run a Google search. Summed up, it's always a good idea to keep them separated at first. Your questions with that are right on track with the guidance I've read as well as with my own experience. Generally I've read that two males will get along well (once they're used to each other), and if you have a female already you should go for a younger, male cat. But ultimately, every cat's personality is different. Here are some sites that I myself used:

http://www.thecatsite.com/a/the-other-cat

http://www.petfinder.com/after-pet-adoption/cat-to-cat-introductions.html

http://cats.about.com/cs/catmanagement101/a/introducecats.htm

http://maxshouse.com/introducing_cats.htm

I hope those are helpful - I thought they provided a good idea of what to expect as well as tips for best mitigating the situation. All in all, your own judgement is best since you already know your adult cat and his behavior. My own existing cat was only 1 year old when I brought home a kitten, and there was a lot of hissing and her prowling after him when we reached the point where he was allowed to explore the house (she even whacked him with her paw if he got too close!). She scared the crap out of him at first (especially since he came from being around lots of friendly playful cats at his foster home), but within a week they were lovey-dovey cuddling and grooming each other. Every cat is different, but have the patience to take things slowly if you need to and everything will be just fine :)

Good luck, and let us know how it goes when the time comes!

Oh yes, kittens under 8weeks or so should be using clay litter without the clumping ability.  I hope your kitten is ok, but I would def contact the vet.