Starting up a not for profit fundraising org

I have been given the task of setting up an organisation for a group of people who wish to fundraise to be able to send people abroad for sports events.  

Please can you advise me the best way of setting this up, whether being an unincorporated association, or a social enterprise.  

I would like it to be as easy as possible as there may be £5000 going through per year.  We are setting up a bank account, and the money will go in and out to pay the sports people whenever necessary.  Will be purely not for profit and all committee members are volunteers.  

If there are any special rules and regulations that I need to follow, please could you point me in the right direction.

Thanks very much, only worked for ltd companies before!