Welcome Isaac!
For starters, none of the written exams need to be completed before starting the program. It is only highly encouraged.
The full list of written exams are:
PAR
IRA
CAX
FIA
FII
FOI
Optionally, you may also take the AGI and IGI.
I recommend Sporty’s Study Buddy for PAR, and Sheppard Air for the rest.
For more information on how to sign up and study for these exams reference: Get Ahead By Taking FAA Knowledge Tests Before Starting ATP / ATP Flight School
Good luck!
Tory