Generally you just keep one seedling per plug. Pinch or snip the extras off at the soil. (If you pull them up by the roots, you risk dislodging the one you want to keep.)

That said, I have sometimes grown 2-3 basil seedlings per pot, but my starter cups were quite a bit bigger than your little plugs (think 3" wide and deep).

Good luck with your rosemary -- it takes FOREVER to germinate! :)

Depends on if you will be transplanting them soon to larger containers like say 4" pot. If so then you can leave all as is. If you plan to leave them in those sponge pod things then the sage and basil would probably do best as 1 or 2 each. The mint is fine as is.

Agree with if sacrificing some use snips, not pulling.

Dave

I've had good luck with leaving numerous basil plants in the same container. If you want more plants you could also prick some out instead of snipping them off and move them to new containers. A little transplant shock but most will survive if done right.