The second place the script is likely for fail is during the build process. At which case it's not the scripts fault, but operator error. Some dependency is missing. The error message will tell what is missing ( the tmp/log file will also list what happened ). Apt-get what is missing and restart the easy_e17. script with "easy_e17.sh -i -s", this will skip re-downloading the source files and will pick-up from where it failed.
Their is a third likely (very likely) way in which the script fails, it os neither the fault of the easy_e17.sh script or operator error, but rather that the eDevelopers are mucking 'bout with some source code. There is not much one can do in this case other then to wait. Aye, one can delve into the failed log file and see if they can sort out the problem. Or one can go to the Enlightenment Forum looking for a solution (good luck with that). I have found that simply waitting till there is a new version is the quickest & easiest thing to do. Just re-run the easy_e17.sh (with just the -i flag) and when it updates the library that failed to build source you should be good to go (or maybe not if the eDevelopers are in a particular feisty mode).
Step 5: Booting into e17.
Well I'm not going to tell an experienced debian user how to login to their system, but the command to start e17 is "enlightenment_start". Any standard window display manager (KDM, GDM, XDM & WDM) should pick up e17 automaticlly, if not then one needs to configure their window display manager of choice by hand. E17 does come with it's own window display manager called Entrance. And last but not least, command line & startx or no window display manager at all.