1) If your US friend's shipping address also happens to be usable as your billing address, you should be fine. Get the gift certificates anyway to avoid lots of little currency conversion charges on your CC account.
3) Sometimes Canadians get books that the US people don't, and some of them are even promotional freebies. It's entirely up to you whether you want to set up a separate account for that sort of thing, or just do all your shopping under one account in the store you think you'll use most.
Possibly Amazon will one day eliminate the $2 Whispernet surcharge as they have for the UK people. But until then, it's incorporated directly into the selling price of each non-free book and you can't currently get around it unless you pose as a US customer. Downloading via computer instead of wireless does not help with this.
The free books never have any fees. The $0.00 you see is the $0.00 you pay, regardless of how you get them onto the Kindle. Unless for some bizarre reason you one day decide to have their files directly emailed to your Kindle using the Whispernet document delivery service instead of just pulling them from the Archives, and then it will cost you.
2) If you plan to go the all-US route and are paranoid about them tracking the payment method for your Kindle, feel free to buy it from your normal account using your regular CC, but have it sent unregistered as a "gift", and then register it to the new account once you receive it.
Or you could do the hypothetically anonymous all GC route if that makes you feel safer.
4) To get books before your Kindle arrives:
a) If you've already ordered it, then if the pre-order is registered to your account, you'll have the option to buy books for it on the store pages. It'll say something like Buy Now With 1-Click/Deliver to "babnaw's Kindle". When your Kindle arrives, once you turn on the wireless, all the books will be automatically delivered to it.
b) If you haven't pre-ordered a Kindle, or designated it as a gift, in which case it'll arrive unregistered, then once you install and register one of the Kindle apps, you can shop away.
The books won't automatically transfer, and once your physical Kindle arrives, you'll have to re-download the a copy of each file specially encoded for it, except in the cases where you bought a no-DRM book.
Most of the classic freebies are no-DRM, and you can just drag and drop them over.
Since sometimes people ask, I'll mention that there is no additional charge for this and you do not have to buy the books twice.
Be sure to check the sticky thread at the top of this forum for any time-limited promotional free books you might like. Most of them are also free for Canadians.
Incidentally, we have some very nice editions of
many classics right here, hand-formatted by our very own MobileRead members and free to all. Though of course the Amazon versions have the advantage that you can sync your reading across several devices if that's something you think you'll be needing.
Hope this helps.