How Much Should I Buy?

I'm about to buy from my dispensary and basically buy a lot (total - about a half oz). I just want different strains around for different purposes (a 1/4 of high-CBD for my normal daily medical toking, some good couchlocking indica, some nice psychoactive sativa) with a few extra grams here or there so I can try different things.
 
I normally would only buy a smaller amount, but the dispensary I'm buying from is basically running a clearance on the high-CBD stuff.
 
I typically don't buy a lot at once, I just buy when I'm close to running out.
 
It's a lot for me, because I normally only buy an 1/8 at a time. I'm worried about storing it and having it all dry out. My average use is that I medically toke at night, but I toke a few times a week to get high. I am also buying a Da Buddha this week so I'll probably be going through my weed pretty slowly, if my last vaporizer was any indicator.
 
Anyone? How much do you buy at once and how do you preserve it? 
 

 

 
Yeah, that's basically my deal. I am getting a little bit of unexpected money coming in and stocking up on all of my consumable items for the next few months. I have been flat broke for the past two months and figuring I'd better stock up on whatever I need. 
 
I don't tend to normally buy a quarter at a time unless it's two 1/8s of different stuff - because I like to try something different here and there.