If I were you, here's what I'd do;
- Create some sample data which would allow you to start to create your sample in Tableau as per your Excel sample you attached. Get it as close as feasible within the tool and understand the limitations you're going to face which will prevent you from getting the 'dashboard' 100% like Business Objects.
- Socialize your prototype with the business and ask for their feedback. Explain the limitations and further refine some real prototypes based on their feedback.
Generally speaking, if you're going to try and replicate a report like this or the business wants the exact same report (give or take 10%) then I personally don't believe Tableau is the right tool. Again in my opinion a report like this is best suited in a tool like SSRS or something which is designed to produce tabular layout reports. Tableau's strength is it's ease of use, 'live feedback' as you develop and visualization. It does a good job with tabular data, but it doesn't do 'pixel perfect' tabular representations. In my experience business users are quickly frustrated by the inability to do things like move headers to different spots, format things in ultraspecific ways, have subtables etc etc.