The first consideration to self mnagement is do the allotment holders want it.
First you must organise a meeting to find out if the majority want to go down this road.
If so, then you ellect a Chair person, secretary, treasurer and committee. have a meeting, discuss a constitution, tenency agreement and rules.
When you have them all finalized you have another meeting and put the committees proposal to the members to vote on.
That just for starters.