The challenge here is:
To understand sustainability
In ways that do not pre-judge what the venture will become. We should not assume that a sustainable fresh expression will look like inherited church.
To sustain the founders of fresh expressions
They need adequate spiritual and practical support.
To birth a venture on a scale that fits the context
You may want to avoid financial commitments that can't be sustained in the long term. Simple church, well connected to the wider church, may be an answer in many cases.
To take seriously the nurture of second generation leaders
Normally they should take over as quickly as possible. As you start, might you shape your venture around the nature and availability of the leaders who might take it forward?
To manage other transitions by going back to your core values
('What are we seeking to do and why?') Agreeing principles that will guide how these values are expressed and giving members maximum freedom to be creative within this framework.
To keep the fresh expression fresh
By regularly reviewing what you are doing, encouraging members to come up with ideas and use their gifts, and constantly introducing - as appropriate - small changes.
Building a Strong Team
Helping the core team (the 'missional community') become not just a community, but a Godly one will set a healthy tone for the fresh expression as a whole. It will involve attending to the following processes:
Forming the missional community, which includes helping members get to know each other better - perhaps using a Myers-Briggs test, for example, and ice-breakers that encourage members to start sharing their lives.
Norming entails negotiating and nurturing communal, task and spiritual norms that will govern the missional community's behaviour and how members relate to each other. It is vital that members cultivate their inner hearts.
Storming is about managing conflict constructively and should be a normal part of a missional community's life. Agreed practices for handling conflict may help (including periods of prayerful silence). The leader must articulate divergent views so that everyone feels heard. Returning to the inner heart to practice forgiveness and make apology will assist teams to become grace-full.
Performing - getting the task done - requires that the missional community pays careful attention to its training needs (eg. mission shaped ministry), to other forms of ongoing support and in particular to the spiritual health of its leader.
Adjourning happens if the team disbands after a time. Sharing what the community has learnt with the wider church may help to turn what can be quite a painful experience into something positive.