Great idea, but you also could present the event for a nominated charity. Ive been organising an event for the past 7 years to raise funds for Cancer Research UK. 12 to 14 different arts take part - had participants from all over the world come along to support the cause but mostly from the north of england. Gets different arts together, increases public awareness in the arts and also the charity. (Raised thousands of pounds over the years - arts becoming less insular and more multi art courses held - also a local martial arts family/fellowship has been created). Still trying to get the idea spread around the uk to get all martial arts clubs/orgs to do similar during the same week (Usually in May) could raise many millions for charity and also martial arts profile nationally. A win - win situation everyway.
Contact all local martial arts/ venue - set date/time etc for event (may be able to get venue etc free if you explain the charity angle)? - agree on a charity - get the charity involved, Liaise with them - publicise the event (dont be coy - get tv, press etc involved - even nationally - never know idea may take off across the country). Very important to ensure insurances are all in order - participants, venue etc. Public and personal liability.
Also so it remains your
idea/project you may want your parents/teacher/sensei or someone you trust to help organise so you dont get the project 'hijacked' by others for their own interests. It can happen.
Go for it! and good luck.