Queries on Rankings

[atptennis]

I am relatively new here & trying to understand the rankings. Can someone please explain the following?
1. I read there are three rankings in tennis. One is national rankings maintained by respective national tennis rankings, followed by ITF rankings (which is Junior rankings, i believe) & 3rd is ATP Pro rankings. Am I correct? Are there any other rankings which I may have miss out?
2. Which other tournaments are counted towards ITF junior rankings, apart from 4 majors?
3. A junior is player below age of 18, right? Can he play junior tourneys once he becomes pro, while playing futures and challengers? As per ITF, any one above 14 years can turn pro.
4. The points earned from junior tourneys, are they counted towards atp rankings? Is there any website where we can see the tournament wise breakup of atp rankings points?
5. I read somewhere that ATP SINGLES Rankings consider points earned from BOTH the singles as well as doubles from futures and challengers. Is this correct?

[atptennis]

Also the points from how many futures and challengers are counter towards rankings?

[Mongolmike]

I don't know the answers, but this might be in the wrong forum. There is a forum dedicated to Juniors and Tournaments, you might get a quicker response there. (I couldn't say for sure because they won't let me in that forum.)

[LuckyR]

The cool thing is, if you are good enough to get a National ranking, you already know the answers to these questions.