Our product team has begun finalizing details for a user accounts project, which will be worked on in a fluid framework. But, responsive web design had just been brought up to the product directors, and now we're realizing it's important to start preparing for it.
Unfortunately, the high-fidelity layouts designed for desktops have just been created, and we haven't had enough resources and time to figure out if we can convert them to smaller layouts, so our directors are hoping we can develop the the whole project in the wide desktop layouts first, and then work backwards to smaller layouts.
So my question is:
Are there some things I should look out for when developing for a desktop first, and then leading to a smaller layout after development?)
Currently, we are going for a fluid layout, and making sure to follow the guidelines of making containers and typography proportionate (percentages and ems)
Edit: Updated my question criteria below JeroenEijkhof's answer