I went at six and made it out, just make sure you be careful in where to level your stats out, it's important in there.
In hardcoe, you're constantly losing health - like literally, you lose health just by being outside.
Every stimpack counts, so Medicine/Survival skills are important in regenerating lost HP. I was level 30 playing on hardcoe and during the initial DLC quests I found myself being squeezed tight in terms of HP/stimpack/food management. It wasn't impossible, but I actually had to be careful.