If you want to develop prototype projects, Blueprint can be enough (even if you won’t be able to access some specific features without C++).
If you want to become a full fledged programmer, C++ is the way to go. Especially since it will necessarily involve doing Blueprint along the road (to speed up your iteration process).
You can also develop large scale projects with blueprint only… but there are many limitations in terms of performances and accessibility to all Unreal features. I wouldn’t advise it if you don’t have a solid programmer background.