I can only provide a partial answer, as we didn't travel south of Cornerbrook, spent most of a week in Gros Morne National Park. The three main villages in the park, Rocky Harbour, Trout River, Norris Pont and Cow Head are all interesting, as are dozens of smaller places in between. Each of these towns have places to eat, things to see. There is still some small commercial fishing out of these places. Just south of Cow Head is where you get access to the boat tour of Western Brook Pond and I'd recommend that. The hike to/from the boat launch is itself interesting, if a bit flat. These places are all on the west coast so sunsets are easier to catch than sunrises. We didn't hike Gros Morne mountain itself, but friends have, and an early morning hike to it might be spectacular. It's pretty much a day long hike, bring food and water.
We hiked parts of the several of the trails in the Park, but it was a few years ago and I can't remember their names. We weren't bored on any of them, and the scenery is very different from what we're used to in central Canada. The info centre is very useful and the guides there will know what to recommend at different times of day. Unless things have changed, I don't recall many loop trails, so you basically come back the same way you went.
We spent a week in Gros Morne park and were lucky with weather. That is very unusual. It's a maritime climate, expect rain.
We never went north of Cow Head, so I can't tell you anything about that. A friend was in St. Anthony's in early July once and it snowed, but that is very unusual. Friends who have visited that Viking archeological site in L'Anse aux Meadows say it was worth the drive.
Btw, estimate your driving times based on 80 kph max, the roads are two-lanes with plenty of twists. No such thing as making good time. We went there twice, once in August and once in June, got rain both trips. Once you're out in the boonies, you'll be alone, not much traffic at all, unless things have changed.
