the "100" is measured in MM, it is the spacing between studs.
When looking for an aftermarket wheel, I'm sure you can get away with anything near a 40 mm Offset. I don't own a '02, but the stock offset should be high 30's to low 40's.
You'd want to keep the overall diameter of the wheel the same, or very close to if you want to keep an accurate speedometer. So let's say that your current tires are 27 inches across, you'd want to find a 17" tire that is close to that diameter.
I'd be more concerned with the wheel width. On my '91 corolla, I have a 7'' wide mag with a 40mm offset. This fits, but I wouldn't go bigger than that. You can play with the offset to run wider wheels, but why bother. 7" is wide enough.
I'll leave the rest of the questions for the newer Corolla owners.
As for the sticker, you can get one made up at your local automotive sticker place for a few bucks. To find the closest place to you, pick out the ricer with the most stickers on his car & follow him

(No flaming intended)