If I where you I would set up a new Site Collection with the Business Intelligence Center template and start to configure it using the guide Set up a BI Center site in SharePoint Online. Then I would continue to read Business intelligence capabilities in Excel, SharePoint Online, and Power BI for Office 365 to see what my options are. If I need to evaluate BI template vs. Power BI I would read Compare a BI Center site to Power BI for Office 365 sites.

For more on hands work I would read both Data sources supported for workbooks in SharePoint Online and File size limits for workbooks in SharePoint Online.

Later on when my BI center is up and running I would consider to enable mobile views reading View workbooks in SharePoint Online on mobile devices.

Hopefully this is a start on you BI Center quest in Office 365/SharePoint Online

If I where you I would set up a new Site Collection with the Business Intelligence Center template and start to configure it using the guide Set up a BI Center site in SharePoint Online. Then I would continue to read Business intelligence capabilities in Excel, SharePoint Online, and Power BI for Office 365 to see what my options are. If I need to evaluate BI template vs. Power BI I would read Compare a BI Center site to Power BI for Office 365 sites.

For more on hands work I would read both Data sources supported for workbooks in SharePoint Online and File size limits for workbooks in SharePoint Online.

Later on when my BI center is up and running I would consider to enable mobile views reading View workbooks in SharePoint Online on mobile devices.

Hopefully this is a start on your BI Center quest in Office 365/SharePoint Online