1) Windows 7. Although some of the Adobe apps will install on windows 7 you may not get the most current versions and infact you will not get the most current version of the Creative Cloud Desktop App (CC DTA) and that will limit which versions can be installed.
2) With only 40GBs of space left on your C drrive that might be an even bigger problem. 99% of all programs today always installs files on the C drive no matter what other drive you actually install the program to. With the Adobe CC DTA to install any Adobe program to some other drive than C you have to make that change in the CC DTA before you install the Adobe programs. The CC DTA will always install to the C drive.