Need help to understand how far APIs can take it us & what the user experience will actually look like?

Hi everyone, we are a rapidly growing startup in the Content Marketing space. We are using a number of tools to ensure we can do everything our clients need in this space i.e. - Content Management - Box.com - Content Measurement - Simplereach.com But would like to pull this all together in one simple tool/project management system (built seperately) with a single login. As such looking for advice as to whether the above is possible with APIs? To understand how integrated we can make all these tools look/feel? And to get an idea as to how hard it will be to make this happen? Thanks in advance!