Dominic,
Welcome on board!
Thank you for thinking of a noble cause.
In our group we have few pilots extremely expert at flying across oceans.
The Flight Academy headed by John Fiscus concentrates some of them. Hopefully they will chime in with advice for you.
I did a LOT of planning for a RTW flight in a Cirrus, but never did it. As others have suggested, join-up with COPA and post in the members section and I bet you will get some good advice.