Decline Bench (with barbell) is great for learning good PL technique. Don't make the angle too steep though. One plate under under one side of the bench will be enough.
Make sure to still arch a bit and don't flare elbows too much. Bar "should" hit somewhere from lower pecs to upper abs depending on technique and how you are built.
And yes, there are def less harsh on the shoulder than flat or incline bench due to the less ROM (if you do them right).@Aidan K
I'd say 495-500 tops. You grinded a bit in the middle so there doesn't seem to be that much left.