newbie lighting questions

I'm a novice at the planted aquarium. I have a 30gal tank that has one
Hagen Aqua-Glow lamp, which is an 18", 15W, K18,000 bulb.

I've done some reading that suggest 1-2 Watts/Gallon for a successful
planted aquarium, which means I need 1-2 more 15W lamps, give or take.

Firstly: Is the lamp I have good? I've searched some FAQ's, but the ones I
read talk about bigger tanks than mine. What is a good Wattage for an 18"
lamp?

Second: Do I in fact need a second lamp to keep my plants? Can I acheive
more efficient lighting and healthy plants with just one lamp in my current
set up?

Third: What is the best way to add light to my tank, if I do need a second
lamp? Do I need to replace my hood? It's a Light-Glo. I was thinking that
I could cut it up, and somehow attach a standalone light to the top of the
hood. My tank is about 12"x24"x12".

Basically, given my tank, what is the best way to get more light into it?

thanks in advance...

G