Welcome!
Make sure to report your crash on answerhub + post your crash log (documents/unrealproject/project name/saved/logs/the file which gets generated after the crash) 
The big file size is because of the avi file type. You can reduce it when you render your movie as jpg files which you put together in a program like sony vegas or camtasia. -> unfortunately atm it’s not possible to change the output file to wmv or any other format (would be cool if somebody knows if it’s possible to change that in C++?) 
https://answers.unrealengine/index.html