You may want to Evaluate SharePoint Online (USA Site) (Swiss Site), but don’t know where to start.

Well, the new IPD (Infrastructure Planning and Design Guide) for SharePoint Online is exactly the right thing for you. The document you are looking for on the web page is the “SharePoint Online - Evaluating Software-plus-Services.zip

All the important facets are explained step-by-step, including a Tally Sheet Job Aid to help you determine the impact and benefits for your users.