Im planning out my perk trees, and have a question regarding
the first perk in some of the trees.

For example, when you look at the pickpocket tree:

Light Fingers: 0-5
Night Thief: 1
Extra Pockets: 1

How many points would it take to get extra pockets? Can I skip
over Light fingers on my way to it or do I have to spend at least
one point?

You have to get the first point.

You can't skip anything. You must travel the line.

Correct, though you only need one perk to do so.

So basically you can have Extra Pockets if you invest 3 perks in that tree.

Most people will do so.

Base carry is 300 so a +100 really helps.

Stamina only helps a little. The formula is (250 + (Stamina/2))

So how it was, three or seven sacrificed perks for reaching "Extra Pockets"?

EDIT: So it was three, thanks Valamyr!

Great thanks.