Would it be okay to only use Dreaming Spanish, read the occasional article in Spanish and watch Spanish series on Netflix? Or do I have to combine it with more in-depth grammar and vocabulary studies?
I am not starting from zero but am not fluent at all.
Do as much as you can, when you can, where you can. However, to be fluent one needs to speak. I know, it sucks, but it is the necessary evil here. You can try a few applications like: Tandem; Conversation Exchange. These places you can find people/groups and chit-chat. It helped me. BUT, my tool was the immersion method, as I live in South America.
-Fluent in Spanish as an English native, living in Chile. Please, feel free to ask me anything!