Looks fine to me. My dog has a similar harness (almost the exact same thing, same brand, the backpack just isn't detachable) and it fits him almost exactly the same. He has a deep Collie chest, though, so he has a bit more room there.
For tightness, I went by if it was sliding around, it was too loose. It should be pretty snug.
For tightness, I went by if it was sliding around, it was too loose. It should be pretty snug.