A lot going on in your plans. Let's being by breaking it down in to the individual components.
Drainage: If you have an issue of water infiltration into the crawl space determine the source. Start by looking around the exterior of the home to make sure that the grade is properly sloping away from the home and if you have gutters and downspouts, make sure they have downspout extensions to carry the water away from the foundation.
If the cause is a high water table, install a perimeter drain tile system with a geotextile sleeve. This drain tile should be connected to a sump and sump pump to remove the water from the interior of the crawlspace.
Ground moisture: It would be recommended that you cover the sand floor of the crawlspace with a min. of 60 mill vapor barrier and then pour over it a minimum of 4" of concrete. This will remove any ground moisture from entering the crawlspace.
Ventilation: I do not recommend natural ventilation for any crawlspace.
- If your home is equipped with a forced air heating and cooling system, extend duct work into the crawl space to mechanically heat and cool it.
- If not, install a humidistat and dehumidifier to control the humidity in the crawl space.
I would also recommend insulating the exterior walls of the crawlspace with a min. of R-10. This will help maintain temperature and minimize moisture build up on surface which are hot on one side and cold on the other.
Duct work: Install insulated duct work, this will reduce moisture from forming on the duct.