Tat2 pretty much covered it. (Tat2 - Chris is that you?)
Do book a room at the electric hotel at Manic 5. Rooms are in atco trailers but clean and it is a nice point to stop take the tour and then get on the gravel the next day. My wife and I went last year riding two up with about 100lbs of gear and found anything above 70km/h was better for the loose gravel, the exception being the sand gravel mix and twisting cow path around fire lake. Shoulders of the gravel will be soft avoid these in the wet. The grader berms don't pose much of an issue, just plow through them. Big rigs are pretty damn considerate and slow down for bikes so you don't get dusted out to badly. The smaller SUVs and pick ups are less so but if you pull over for lunch or pictures you can pretty much guarantee ever vehicle will stop to make sure you are ok. In Church Hill Falls you camp on the lawn of the church, though there is a small hotel. CHF is a company town but pleasant enough, even has a little bar to have a pint. The dam tour is pretty cool too.
Not sure how far the GS can go but my GSA had no fuel issues. We ended up linking in with a group of KLR riders and a BMW 650GS and all of them made it without issues.
The trip is mostly about the road as there isn't a lot else to see, but we made a point of hauling over at rivers and lakes for pics and to get off the bike for a bit and enjoy the area. Bring a bug jacket BTW with bug hat, the flies are thick. People are more reserved in Lab while in ND they are outgoing and friendly, meeting all the rumours you hear about people from the rock being some of the most colorful characters and friendliest folks in Canada.
We met a couple on the Lab side of the Lab - ND ferry. They were in a day trip on their Goldwing and when we asked about camping on the other side as we did not want to ride at night (don't ride at night) in the end we ended up riding at night but behind his GW, followed by 7 of us. He and his wife put all of us up for the night, made breakfast and then took us out for a few hours of iceburg watching on their boat. Would not take anything more than thank you for their kindness.
I ran TKCs front and rear and although the rear was well worn out when we returned to Halifax (start point) it was nice (but not necessary) to have the knobs on the dirt part.
Final thought, "when in doubt gas it out" proved to be the best way to deal with any wobbles on the dirt, If the front starts to wobble around and go for a tank slapper roll on the throttle. Conditions very considerably and although any one stretch is not hard core riding by any means, the distances demand you stay alert and pay attention. People of all riding skill get hurt and killed on this road every year.
BTW 120km/h is about right for the GSA, nice and stable, even faster might be too but my pillion didn't like it.
I guess an off at 80km/h is much different than one at 120 + km/h
I want to take my KTM there with a chase vehicle and have a go