5 year business plan

We are a 4 year old ‘supergroup’ , 3 independent practices with single TID and shared back office, and are having issues with leadership transition. Our very competent Managing Partner is looking to transition out of that role and none of the other seven partners is interested in assuming the role. The BOD wants to jumpstart the transition process and we think a Five Year Business Plan discussion would allow us to identify the issue and put it in the context of everyone’s best interest. We hope a transition plan would naturally spring from the discussions. Does anyone have a resource that would guide us in the process of developing a Five Year Business Plan?