Hello, thank you for your question. A primrose is actually the common name for another type of flowering plant, did you have a question about that? Regarding rose hips you can prune any time after flowering. If you want the rose to re-bloom the sooner the better. If you're aiming for harvesting the rose hips you'll want to wait until they are bright, shiny red and have not begun to wrinkle (depending on how you want to use them). Let me know what additional information I can help with, 

Best, 

It looks like this is one of the wild type roses, so you really don't have to remove the hips if you don't want to. It's not a primrose however. If you do a google search or primrose you can see that they are an herbaceous plant, and in different families to the rose family. Common names are tricky that way! 

RE coffee grounds, if used as a mulch which from your description sounds like the case, it's not going to make a substantial nutritional difference for most plants.

Here's a great resource for coffee grounds in the garden: https://s3.wp.wsu.edu/uploads/sites/403/2015/03/coffee-grounds.pdf 

Let me know if you have further questions, happy gardening!