1. Yes, the dark red arrow represent the first migration from the Hallstatt region to Italy. I believe that there were several migrations from the Alps region during the whole Hallstatt and La Tène period (1200 to 50 BCE). I didn't want to cluster the map so I stopped around 1000 BCE, at the beginning of Hallstatt. There were already other arrows of previous migrations to Britain, France and Iberia, so it would have been difficult to read.
The main purpose of this map is to show where R1b originated and how it spread to the different parts of the world where it is found nowadays, in a chronological order. R1b-S28 in Britain or Iberia is only a minority of all R1b and therefore it wasn't so important to display it.
2. Most of the R1b-S116 in Scandinavia, Greece and Iberia is still simply R1b-S116 nowadays (or at least subclades haven't been identified yet). Scandinavia has the particularity of having a great diversity of minor subclades (S21, S28, L21), which all probably came from Germany. S28 is likely to have come during the Hallstatt period, while S21 came earlier. I am trying to figure out when L21 arrived in Scandinavia. L21 and S28 are both more common in southern Germany, while S21 is more frequent in northern Germany, so it is possible that L21 was part of an early Hallstatt migration too. However I am inclined to think that L21 correspond to an even earlier migration from southern Germany, maybe around 2000 BCE (same time as when L21 supposedly went to Britain).