Buying a 2019 Mustang GT—Good Deal and Infotainment Upgrade Advice?

Hello hello…

I wanna buy my first Mustang—a 2019 GT with 31k miles on it. The asking price is $35k. Does this sound like a good deal?

Also, I’m thinking about upgrading the infotainment system. Does anyone have any ideas about the costs involved?

All suggestions are welcome. TIA