Short answers for this trip. Weather, roads, and aurora refresh through the day.
South first is the popular direction — counterclockwise on the Ring Road (Route 1).
Most short trips leave Reykjavík and hit the south coast (Seljalandsfoss, Skógafoss, Vík, Jökulsárlón) before the north or east. Weather is usually a bit milder, the famous waterfalls come early, and you are not fighting the full-ring crowd on day one.
Clockwise (north / Snæfellsnes first, south last) is quieter at those same stops later in the day. Neither is “wrong.”
This trip is not a full ring. You do: - Day 2 west — Snæfellsnes out-and-back - Days 4–5 south / east as far as Jökulsárlón, then back - Day 6 Golden Circle
Skip the north, East Fjords, and highlands. Stay on paved Route 1 / 54 / Golden Circle roads. No F-roads.