Hi Brigitte. I guess all of this is very much dependent on how you work and where your ideas come from. With my current WIP I started with setting as I often get inspired by places. In this case it was a big old rambling house overlooking the sea. I wanted to set it in the 1970s and had an idea of plot but then I put everything on hold a while and as you said, worked on the characters - hundreds of questions for each of the main characters which then gave me an idea of their backgrounds and that then fed into the plot. I did lots of research on the era which is also feeding into the plot. I then wrote a first draft but now I've done some research into myths and am feeding that in to the rewrite ( quite a big change)
Basically, yes, I did a lot of work on the characters before I plotted but I know others just develop the characters, put them in a dilemma and write. It's what works for you.
But if you're stuck, yes try getting to know your characters for a while - you might find they inspire something plot wise tits never considered.
And I do sympathise with your plotting dilemmas - thinking of the big picture makes my head hurt!