After go through different required portion of code of jorani.
This weeks generally passes through planing period, which include planing of following point.

The user create/edit forms should have a new field(s) (impact on DB model).

2 levels or multi-level? If multi-level, what is the workflow exactly? I mean the order of the managers is important or not (AND or OR)?

What about the different emails sent
Is there any change into the WebUI besides the user management part?
What about the reminder email?

how to implement short leave feature?