Hello everyone! Just want your thoughts on a few things.

My current situation: IPhone 7 Plus since 2018 - battery health 75% and thinking of buying a new iPhone.

First case scenario buying a second hand iPhone 12 Pro Max with 84% battery health for 620 USD ( currently have 700 usd budget) would that be a good deal? I plan on using the phone for the next 5-7 years. I also plan on replacing the battery for 100 usd in an Apple approved shop which would cost me 100 USD.

A couple of questions: 1.) should I pull the trigger? Is a 12 pro max gonna be good? 2.) Is it possible to have the 13 pro max battery out into the 12 pro max? 3.) should I just continue to save money to get a 13 pro max eventually for 1,140 USD? 4.) What are the things I need to look out for when buying a second hand phone becuase this will be my first one?

Thank you everyone! Ill appreciate any reply that would help me current situation.