I have lots of questions about crawlspaces that I want to understand, and
need a reference for this topic.
Among other things, I wonder about radon possibilites, humidity issues,
suggested ways to counteract these problems, ventilation suggestions,
etc. I want to use this large area for storage, but foresee trouble.

When we built our house (2003-2004), we were required to have 1 square foot
of perimeter venting for every 150 square feet of the crawlspace, placing
vents as close to the corners as possible and providing cross ventilation
(so you get air movement through the crawlspace). We added a few extra
vents just to be safe.

The ground in the crawlspace also had to be covered with a layer of 6-mil
plastic. I installed a 2" layer of pea gravel before laying down the
plastic for better drainage and to prevent small sticks or rocks from
poking holes in the plastic. It's also a bit easier on the knees when
crawling around down there.

The ground outside the house should slope away from the house to direct any
surface water (rain) away from the foundation. Make sure gutter downspouts
are directed well away from the foundation too.

If you have a high water table, or water is otherwise getting into your
crawlspace, you should slope the ground in the crawlspace to a point where
you can install a sump pump to pump out the water (away from the house, of
course).

The foundation walls should be waterproofed on the outside, and you should
have a perimeter "french drain" running around the house to take any water
that finds it's way down the foundation wall out away from the house,
instead of getting into your crawlspace.

We live in Washington state where we get lots of rain, and our crawlspace
is nice and dry.

If you plan on storing anything down there, be sure you protect the plastic
vapor barrier so it isn't damaged. Maybe planks set up on blocks or
something.

Good luck,

Anthony