Hi MSFTFan,
I will try my best to answer the questions for you.
Office 365 Home Premium and Office 365 Small Business Premium are two different products. Office 365 Small Business is for business, but Office 365 Home Premium is for home. Therefore, yes, you need to cancel your Office 365 Home Premium and then to subscribe Office 365 Small Business Premium.
Sorry that you cannot use the same Microsoft account with the Office 365 Small Business Premium, you need to create a new Office 365 account (xxx.onmicrosoft.com).
Yes, you need to move manually the files stored in SkyDrive associated with your Office 365 Home Premium subscription to the Office 365 Small Business Premium account's SkyDrive Pro library.
Sorry for any inconvenience caused.
Best Regards,
Anna Shi