If the phone shows up on Apple website with valid warranty, that itself authenticates the dealer as reliable (Although, it doesn't matter as Apple is the one which will be fulfilling the warranty)
Yes you can. Till the time you have sufficient (100% of product cost) Amazon pay balance in you account, you can use it to purchase anything on amazon.
Note: Amazon pay balance cannot be used partially with any other payment mode.
I want handy and lightweight phone thats why 16 pro.
I can wait for 17 also but apple planning to use own modem and wifi chips ditching QCOM BCOM so dont want to buy 17