I can help out a bit here. See my trip report link in sig.
1) Take more time or cut back your trip. Do some things beside sit on your butt on the bike 8-10 hours a day. Otherwise, you might as well stay home and sit on a sawhorse in your basement and watch videos.
2) The new road is open between HVGB and Cartwright Junction. Parts of it were awful last June, but later trip reports note it as complete - i.e. it's in as good shape as the rest of the TLH.
3) It's ~400 km between gas in HVGB and Port Hope Simpson. Plan accordingly.
4) As someone else has noted, the north shore of the St. Lawrence is a nicer ride than the south shore.
5) In Churchill Falls, take the hydro plant tour. It's cool. It's free. Eats up all of half a day. Ask at the gas station for the phone number. Anyone who passes on this is a fool.
6) Consider taking the hydro plant tour at Manic 5 too. (They hadn't opened yet when I was there.)
7) Good place to stay in HVGB if you need one: TMT's B&B. When you hit the "T" and have to chose between turning left toward GB or right toward HV, turn left and go 3 or 4 km. It's on the left. Unpretentious, cheap.
8) Bring good bug spray if you're camping in August.
Good luck and enjoy the adventure!