The text for Dr. Strange says:

Astral Form: Give Dr. Strange a power action. Place a GG #014a or GG #014b Astral Dr. Strange from outside of the game in an adjacent square.

Since the Astral Dr. Strange is from outside the game, I assume its cost does not need to be included when building my force. Is this correct?

Thanks for the help!

You are correct.

If they KO the Astral D-Strange, would they get 13 victory points?

Defeated characters are scored, yes.

So think very carefully before you duplicate Madrox or summon an astral projection... you could very well be helping your opponent defeat you.