Technically, we are pointing you to three resources here. Math was never our strength.
Before you buy, of course, you’ll want to get a quick look at what plan offers what features. Compare Office 365 for Business plans.
Then check out the Microsoft TechNet Office 365 Service Comparison. (Hopefully it's kept updated--it's quite detailed.)
Both are also useful after you buy Office 365, and you wonder why the feature you want isn’t showing up on the plan you chose.
Say you want self-service BI and the ability to query data with Power Query, analyze data with Power Pivot, and visualize data with Power View and Power Map. Why isn't it on your plan? (Hint: Maybe because you chose Enterprise E1.)
So then what? You got it--you go to the page that tells you how—and if you qualify--to switch plans. Switch to a different Office 365 plan or subscription