A:AnswerDepends on the phone. A newer phone may net you a couple of hundred....old phones like 2 versions behind or more, nothing. Call first and ask them about your phone specifically.
A:AnswerYou can buy an unlocked phone which you can use on any carrier (service) but I don't think you can set up a payment plan with Best Buy. The monthly payments are offered by the carrier (example Verizon).
A:AnswerThe iPhone 8 Plus is bigger than the iPhone 8; otherwise they are essentially the same.
See https://www.trustedreviews.com/news/iphone-8-vs-iphone-8-plus-3286235
A:AnswerWell I had an iPhone 6, 16GB in excellent condition and I upgraded to the 8 plus last month and the trade in was $65. Sales person enters in your model number to get the trade in amount. So your 7 will be more if in excellent condition. By the way, Best Buy had a better price than Verizon for iPhone and trade in at that moment in time. Hope this helps.