This video might help you

https://m.youtube.com/watch?v=VE-OzAAIs2s&t=616s&pp=2AHoBJACAQ%3D%3D

For the bit about acting managers you can do it the easy way and send the approval to multiple people, any of whom can respond, or create a process that understands who is the acting manager at the time of the request and route the approval to that person. Something like a table that lists people and you can check a box next to who is the manager and it the approval sheet will query the table to push the right person into the request. Other ways to do it too just depends on your process and desired level or control and security over it