Regarding the stocking up, that's something I kind of struggle with when talking with a newcomer to e-smoking.
I personally have an embarrassing number of 801 and 901 atomizers, and a decent supply of 510s. That's because I have a Screwdriver that I'm very happy with (takes the 901), a JantyStick that I think is positively nifty (takes the 801), and I have about 8 batteries I rotate plus a USB passthrough battery for the 510 (which I dearly love).
I've stopped buying 901 and 801 batteries because I simply don't use them anymore. (I'll even be phasing out on the 510 batteries once I acquire a 510 adaptor for my JantyStick.)
Basically, I'm at the point now where the stuff I've stocked up on, well, I KNOW I'm going to use it. I'd be feeling kind of bummed if I had stocked up on 401 parts, an e-cig that I tried but quickly tossed aside when I got tired of dealing with the refilling of teeny-tiny cartridges.
So you hate to stock up too much until you're fairly sure that the parts you're ordering are parts you'll continue to use. On the other hand, you never want to find yourself down to one spare atomizer. 8-o
For those who are just starting off, I think I would suggest having maybe 2-3 backup atomizers and then 1-2 backup batteries. I personally wouldn't want to invest more than that until I was fairly committed to a particular model.