Your project files are not part of the app. Why would you loose them?
CC will open older projects from CS5, but, if you have the drive space you might want keep CS5 installed for a while.
Make sure that CC will install on your OS without problems. We don't have any idea what kind of system you are using so that could present a problem installing CC.
I have both CS5 and CC installed on my home machine (Windows 7) with no problems.
I see no reason to uninstall After Effects CS5.
I have After Effects CS4 (9), CS5 (10), CS5.5 (10.5), CS6 (11), and CC (12) all installed on the same computer.