Let me present a scenario.
A small company has 6 mobile users that have 6 laptops spread across the country. Two of the users use their personal laptops and the others have company issued. There is no physical location for this company. Some users have Windows and some have Macs. They don't have a central server. The 3rd party applications that they use for their data is Salesforce, dropbox and another one. They constantly email each other with sensitive items in excel and also use slack to communicate. The concern is data security and making sure there are no compromising behaviors with a need to utilize best practices.
What are some ideas to make sure data remains safe when emailing one another and sharing information? Would it be a smart idea to utilize Office 365 in this scenario and keep all documents in One Drive or SharePoint? Should I consider Enterprise Mobility + Security E3? Or are there other methods to utilize security considering there are Macs in the picture?