Hey Giriraj,
I'm not completely sure what your actual business requirement is.
Sadly we don't have a way to toggle mandatory flag (well not without customisation).
Guessing what they really want is to show/hide fields as applicable to the stage in lifecycle.
If that's right you've got these options:
1. put them in sections, have a process open/close these as you want (i'll share at somepoint)
2. In new UX use blueprints, you can switch the blueprint at different stages via process and thus control what is shown
3. use sub pages, have them show/hide based on rules
4. build a custom web app and integrate into the page
As for launching a process when the page loads, there's a way via the menu actions with some tactical javascript
I personally wouldn't recommend this approach though!
hope that is of some use
Andrew