I'm deciding on building my own 2x10 bass cab, but I have some questions first.

I have a Fender Rumble 100 and I'm wondering if would need a power amp so I can power the extra cab.

Because if I understand right, you want to have the cab rated for a little more watts than your head and you need enough watts to power the cab so you can actually get most of the sound out of it right?

And to hook them up would I go from the line out of my amp to what in the cab?

Those are some of the questions I have for now. I'll probobly have more later once I get some of these facts straightened out.
Bass is my life.