I'd recommend having a trustee, chairman (last two often combined), maintenance member, treasurer, and consider having somebody responsible for organising regular cleaning as well. Have some mechanism for rotating those roles so that nobody feels all the work is dumped on them indefinitely - ideally nobody wants to do these jobs for more than about 3 years a time.
That's a wonderful idea but, in practice, probably impossible. For a start, having a Trustee is a legal requirement and the person has to be registered with the CAA along with the members of the Group. The CAA charge for changing the name of the Trustee but not the names of individual members. However, I do like the idea of a rota for being responsible for aircraft cleaning although, even that job can have small complications such as an agreed procedure for cleaning critical items such as windshields etc. You will be very lucky if you have one member with the specialised skills to ensure that proper maintenance is carried out and, particularly, to work out the best action in the event of minor problems which occur from time to time.
Another issue which makes changing jobs a bit less viable for Permit aircraft is that each group has to have at least one member who has full membership of the LAA. The rest can be ordinary members which is about £50 cheaper.