The Governance is pretty much determined by the Companies Act 2006, the Memorandum of Association and the Articles of Association. There are members who elect a board at the AGM and the board runs the charity. The members have certain additional powers which can be exercised in writing, at AGMs or at EGMs. "Member" is this context means "guarantor member". The part that isn't settled yet is membership fees and what forms of membership we'll have (if any) in addition to membership of the company proper, but whatever is decided, they won't get a vote at AGMs. Having 100s or over 1000s of members shouldn't be a problem - most will probably vote by proxy at the AGM. There are public companies with 10s or even 100s of thousands of shareholders that manage just fine, the vast majority just fill out a proxy statement that is sent to them in the post and never go near the actual meeting.