Smiller answered well for 2 and 3.
Regarding 1, i'm assuming you live in the US and therefore I can't help you regarding the best vendor 'cause i'm from europe.
But still, my 2 cents here : if the error is hardware/software related, Dji is most likely going to repair or exchange it, no matter who sold it to you. The vendor won't be much help to you.
However if the fault is yours (like it is for most of the failure as far as I understood), Dji won't cover it and you'll be on you own.
I'm strongly thinking about getting a full insurance for theft, damages and loss on my bird. As far as I know, here in France, it's something like 300 or 400€ a year for full coverage.
It's quite a lot of money - but then I would feel so much more secure if I had it, and I might end up doing better shots because i'm not always scared of loosing it !