Hi, M.EContracting,
This is my first day of joining this community and i came across your query. And it would be my pleasure if i can help you in any way. I have technical expertise in Office 365.
So after reading your query i must say that you are on the right track now every one is moving to Office 365 whether it is of small or big organization. if i am not wrong and i am clear about your query then you want to move the Exchange outlook 2007 to Office 365. Only then I would like to suggest you to use automated tool to solve and do migration from your old exchange to Office 365.
I have tried and tested one of the out standing tool in my Exchange lab to do Exchange Server migration. This tool has too many advanced feature by which you can do job in a single go.
To know more about this tool and to understand the feature of this tool you have to visit at www.lepide.com/exchangemigrator. It will help you in this complex mailbox migration to Office 365.
I hope this will surely help you and let me know if i can help you any other way.
Thanks!