I guess you've got all the answers you needed on the WhatsApp Clyde but everybody's not there.
We drove av SUV not a 4WD, but you can do it with at normal car (not a low sports car though). The gravel roads are good on the Trans Labrador Highway, the gravel is not very loose gravel. They work on paving the remaining gravel roads, so in a year or two the gravel are history. I think we did round 60-70 km/h (or 35-45 miles/h). After 400 km on the gravel - you're in heaven - driving on paved roads makes it beautiful silenced!
The itinerary itself I must credit Randi, she worked it out, but i suggested on joining them as one trip.
The long streches is what most people dislike in our itinerary and we had a couple of those. It was one into Labrador and one into The Northwest Territories, both northbound and were round 1000 km long. I can understand that going alone on such a strech would be a hassle, but going as a pair its just a matter of attitude. We live in Norway, it's the edge of Europe. Going to central Europe is about 1000 km sometimes more, so we're kind of used to such distances. I relax when I'm driving - and drive more than Randi, but when I'm feeling a bit tired Randi takes over. We have al ot of music, audiobooks (that's important), quiz games and we just enjoy each others company in the car. Also we usually bring lunch along and stop for picnics. The difference between going south to Europe and north in Canada is a kind of explorer feeling which I like, and as you enter "no mans land" there are unpredictable wild animal life - seeing a bear along then road is a thrill.
We were warned about insects, and I didn't look forward to being eaten my a million mosquitoes. The snow usually disappear early June up here - and the insects needs another month to appear i seams. We saw very few insects in Labrador and Newfoundland (late June), but there really a lot in Northwest Territories (mid July).
The strech from Labrador City to the east coast its another 1000 km, but we split it in two parts. Labrador City is a small community but Happy Valley Goose Bay is a bigger - and we stayed overnight there. It's a little more interesting to explore than Labrador City. Arriving at the east coast - just north of Red Bay - gives you a satisfactory feeling - a feeling of an achivement. Really - it's nothing - just driving - but still a good feeling. From this "starting point" up north - it's a piece of cake "collecting" the WHS's "down the road". Well crossing Newfoundland is also a strech of 1000 km or more, but this "continent" is more inhabited so stopovers are more easy, and the lobsters are just delicious.
There are two ferries to Nova Scotia, one from the east part of Newfoundland, a voyage for about 15 hours, and one from the west part, about 6 hours. We would prefer the eastern ferry - not far from Mistaken Point - but we where to late booking it so we had to drive back to the western part.
Cruising around Nova Scotia, New Brunswick and back to Quebec is just "a walk in the park"!
And don't forget - the lobster capital is Shediac New Brunswick.