I would recommend you visit the lawn forum, as they are really into lawns, and the organic forum as well.

Grass does not need fertilizer in the summer. The weeds might appreciate it. Your friend was probably talking about Scotts system 1 thru 4. You put down 1 in spring, 2 in early summer, etc... My MIL had me do it for her one year. It didn't make much sense to me to be applying a chemical to the lawn for which I had to wear the recommended face mask.

You need to think about on what kind of effort and $$ you want to spend on the lawn. You should also consider what your stance on organic vs. chemical is. Do you need/want the golf lawn, or is a few weeds acceptable if you can avoid all the chemicals? (Weeds need less water to keep your lawn green during a drought!)

From what I've read, you need to mow the lawn to 3", and let the grass shade out most weeds. The grass grows very fast to reach 3", and then slows up.

The problem is most people cannot stand the shaggy look, and would prefer to scalp the lawn.

Our neighbors had a beautiful lawn with the grass almost at 4 inches. It was always dark green, and lush. They sold, and the new owners cut the grass to about 1 in, and immediately had problems. Uneven coverage, lots of weeds, it looked terrible.

I think to have a perfect lawn requires chemicals and lots of water. I cannot justify the chemicals (which can be tracked into the house and remain in carpets for months) or using the precious resource of water just for a lawn. But that is my opinion.