If your doing Helgen totally vanilla I'd be perplexed at a CTD at that point. You should, IMNSHO, play vanilla until the quest is "completed" on the other side of Helgen. If you are starting with mods, LOOT and SSEdit are a must, and Wyre for that matter. If you start out with too many mods and are inexperienced, it may be difficult, to say the least to track down the conflict causing your issue. I started once with STEP mods from the beginning. Bad idea. For me anyway. Once I had a clean save then I started the painstaking process of adding mods, looting mods and ssediting mods. I also recommend Bethini and ReSaver. Don't give up friend, just start small. After 2 years of Oldrim and SSE (everything I ever learned about modding I learned right here on Nexus), I'm now up to 160 mods, crashes are rare, and lately only one conflict I didn't catch before I installed it. I have learned to almost enjoy the challenge of piling on the mods without a crash, but it's a careful piling. Learn the dance of modding and crashes are just a blip. Good luck!