You've certainly gone and done some homework.
I would make one point about this statement
(*note by me, the landing roll distance doesn't change with altitude)
Landing roll will increase with altitude. This is because TAS increases relative to IAS with altitude. Even though you are touching down at the same IAS your TAS hence Ground Speed will be higher and it will take longer to stop.
Otherwise you have done a good job of educating yourself on approach and landing speeds.
P.S.
The 1.3 Vs target threshold speed I mentioned in one of my earlier posts is the the minimum speed legislated for crossing the threshold.
Many POH landing performance figures are calculated using this figure. If this is the case you will need to fly this speed to meet the book figures.
It looks as if Diamond uses a higher figure than 1.3 Vs.