“Let’s start with the FBI, for instance. What exactly would he do?”
If Trump was sincere about stopping that corrupt crime organization, he would simply sign an executive order abolishing it since it was established using an executive order.
Hind sight is 20/20, which is why everyone has an opinion. President Trump is the man in area with his face covered in sweat and blood. He doesn't have the luxury of your armchair.
You may recall a time when Jeff Sessions was considered an excellent choice by all the people now critiquing Trump's personal choices.