Is there meant to be a picture?

Yes, I’m not sure why it didn’t load.

In the last picture, due to the distance to the subject we can't tell how much space is available for a plant.

At the long strip, it looks like a good bed for a mixed run of hybrid daylilies, as they are tough plant and there would be some color there during the summer season. If the mix is varied, bloom can extend for a few weeks. But how are you going to plant with the rocks? I'd remove them and use regular wood based mulch. Also, the weeds could be easily killed with weed killer -- Round-up specifically. You'd need to keep them away and Preen, applied regularly per schedule, would be helpful for that. But you absolutely have to hand pull what returns or the problem will never be solved.