You must have done proper manpower planning; only then should you get these 100 positions. Now categorize the positions into different categories like replacement positions, backup positions, development positions, and operations positions.
Now, grade positions - replacement positions would be top priority as the current employee has left, and in order to handle one's work, you need a person unless and until another employee is rotated to that position.
You can place backup positions on a temporary basis with lower priority as currently, a person is available to handle the profile, and you will require a person only once they leave.
So, you can categorize the openings. After that, you will be required to grade the openings within one category itself and interact with managers and business managers to understand the requirements more precisely.
There is a different kind of fun in working simultaneously on different positions, as in one job posting or interaction, you will come across different profiles that will help you in closing other positions. So, enjoy and good luck.
In case of any problem, do write back.
Regards,
Seema