Arduino Uno to Control PWM Fans?

I meant auxillary power as in another molex.

And I only plan on getting as low as about 30-40% fan speed, so the motors shouldn't have a problem.

So it is assumed we know how you plan to connect the molex ?
I didn't see that mentioned in your post. Are we supposed to know what you mean ?
I mean if it is so "simplistic" why are you posting here and what are you asking for ?
Is there a question here somewhere ? I didn't see any question marks.