Newbie Question: Gravel Depth and Aeration

A few questions for you guys today.

I'm setting up a 33 Gal 36" x 12.6" x 18" (Hagen All-Glass A-3023) tank
soon, and I'm getting all the bits and pieces I need, but I can't seem
to find an answer to either of these questions through Google.

How deep should me gravel be? This is a freshwater tank, and I know it
should probably be a darker colour, but an exact depth is never really
specified anywhere I look. Is 2 inches (average, I know it should be
varied) too much? Also, is there a magic formula I can use so that I
don't end up buying too much extra gravel? Would one 25 pound bag do
the job?

Second question has to do with aeration. In the tank I had when I was
little, I had an air stone to help with aeration, but no filter for a
long time, so I think we just kept the air stone, because we didn't know
that a hang-on-back filter could aerate as well. My question is, is the
filter going to do the trick for aeration, or should I get an air pump
as well? The filter I'm using is an Aquaclear 200.

Thanks for any info you can provide!

Gord