1. They suggest rice cereal to begin with, however some babies just don't like the taste. See how that goes for a few days, if he doesn't like it, you can put puree fruit/vegies in it. I personally would sterilise everything.
2. I started giving Nina water from a sippy cup at 4 months. She'll only have 5-10ml, so not much at all, but it's just mainly to get used to it instead of a bottle. And I sterelise the cup after each use.
3. I think so. They're only having a small amount of food.
4. I think mid morning, that way if they have a reaction to it, or it doesn't agree with them, you can sort it out during the day, rather than having a long night with him. I think you should give it to him the same time each day to begin with.
5. Wait until you feel satisfied he hasn't had a reaction to it, and that it agrees with him. This could be a week or two.

HTH