Best practices for old plans, portfolios, account managers?

Hello,

My organization wants to refine our use of plans and portfolios. We have hundreds of constituents in which the account manager or primary worker is no longer with the company. We also have many steps from previous campaigns that are still open. 

We would like to close all of the irrelevant steps and replace the account managers with people who currently work here. I am not sure if primary workers need to be replaced on old steps. I would assume not. 

What steps would you take, or have you taken, to clean up such a situation?

Thank you,

John