To use DE here is information
FIRST WEAR A MASK when handling the DE, like putting it on the chickens floor 
or making a dust box with it 
3 lbs of sand or soil 
1 cup of de makes good dust box when they get older 
I would think it could be stored in the sack in a garbage can with lid 
then the moisture won't get to it 
It will not harm the chicks but as you wear a mask maybe don't throw it around crazy like 
but be more careful when putting it down as they will be in there 
I think that I would do a section like 1/4 of the coop and then after the De put the beding on this amt 
then go from there to finish the De and bedding 
as the chicks will tend to stay in the new bedding on the floor 
while you are putting the rest down 
always keep the DE then bedding between you and the chicks 
It is 2 parts DE and 8 part feed every day
if using a cup measure then do that 
any questions email me 
--------------------------------------------------------------------------------