Yes, it’s safe to buy from the Amazon when the seller is an authorized DJI dealer (like the link I shared above). There are some dealers selling on eBay too, but they are a little more expensive. Like this one:
From Amazon? Many times. The right side of the product listing on Amazon shows when the product will be delivered.
No. Your batteries should last a long time if you follow these tips.
It is if you need to charge the batteries in a car. I’d personally buy enough batteries to last for as long as I needed to fly in a single outing.
I don’t use 3rd party batteries. DJI batteries work well and they don’t void the DJI warranty (assuming the Phantom is still under warranty).
If I ever change my mind and decide to start using 3rd party batteries, I’ll use this brand due to their consistently good ratings:
https://www.amazon.com/Powerextra-Intelligent-Replacement-Professional-Advanced/dp/B01GZZY1B2