I don't think anyone can give you a clear answer, given that the effects of coffee depend on complex mix of factors, like caffeine metabolism, metabolism in general, brain chemistry, and so on. However, it is known that stimulants generally shorten the attention span, so a good guess would be that you indeed are in or close to the "normal" zone.

Perhaps. Although even the experts don't fully understand ADHD.

Most people don't know where they fall on the ADHD spectrum. Maybe that's one of the reasons why there's such a mixed opinion on whether caffeine is good or bad when it comes to focusing.

Oooo. I need to read this.

http://www.pediatricneurology.com/adhd.htm

Or would you recommend another source?

Note to self: reading medical textbooks means you always have the symptoms, so you are always ill.