Setting up my own (charity) marathon swim

Hello folks, I am beginning to look into setting up, and doing a marathon swim for charity, for next summer, (solo) and I was wondering if anybody here had been through it and had any input. I am planning on getting in touch with coastguards, etc. in order to get whatever permits I need, and finding information on currents, etc. to pick a time that will be ideal for the swim. Beyond these, I'm sure there are many other obstacles that will come up. Any help along the way would be great. Edit: In case it wasn't clear, I am planning on having the only one swimming to be me. Thank you!