Because the computer is new I suspect that it is the Lenovo Ideapad Flex 6 (14-inch) which has no optical drive for installing the program, this means that you will have to create a Microsoft account and download Office 2016, all the info that you need is available at the link that was previously provided in my reply #2.
Yes leave the Lenovo software for now and up until you have Office 2016 up and running.
It depends what data you want to transfer, music, pictures and videos can be safely copied across but programs will have to be clean installed, the capacity of the storage device on the computer needs to be considered, if it is only 256GB you should consider getting yourself an external USB hard drive.