Working with solutions

On Org1
I have core solution as unmanaged

On Org2
core solution as managed
custom solution as unmanaged

On Org3
core solution as managed
custom  solution as managed
custom2 as unmanaged

Stagging
core solution as managed
custom solution as managed
custom2 solution as managed

if there is an issue in custom solutions, then I work on Org2 and mitigate the issue and export it as managed and on Org3 and stagging import it as managed with overwrite existing customizations and selecting the checkbox of active process and messages, otherwise it will give a good pain to enable all the steps.

Any step which is changed which was part of managed solution will be overwritten

if when trying to import solution gives error that some pluin is missing then register that pluin using pluin registeration tool and then import managed solution, and then select appropirate options.