Austin

Its a good idea to have 3-4 atomizers on hand for just in case. I usually order a couple a month. currently have about 10 (maybe more ) on hand --just in case !!!

No help with shipping canada, sorry.

Dripping = 2-3 drops to atomizer is good for about 6-8 draws. dripping does require more frequent steps, but for me anyway, Its worth it. you can drip 2 drops to the atomizer and replace the cart with liquid in it and you will be good to go. if you use a cart with filler and liquid, you won't have to drip quite as often.
When the flavor changes or gets a burnt taste you need more liquid. if you are dripping its hard to run the atty too dry--the taste is horrendous. You will quickly learn the flavor/vapor changes and when to drip. Honestly, I don't even think about it much anymore, its just becomes routine.

billing address is where your CC is registered, probably same as address

You pay with your credit or debit card. Some sites use Paypal but not many.. Last time I used Totally Wicked they did. So if you only have the paypal account you need to look around to see what vendor takes it.

Yes, you can use your debit card(at least as far as I know). the billing address is the address your card statement is sent to--usually the same as your shipping address. 'The amount is taken directly from your credit card or debit account.

you can also use the visa gift cards if it won't accept your debit. can get those at most grocery stores or walmart.