If we land in Gander, we could also concentrate on Twillingate and Trinity/Bonavista...

Can you fly into St. Johns and out of Deer Lake?

I agree with caperace that it would be good to fly in to St Johns and out of Deer Lake.
IMHO 3 or 4 days in Twillingate would be too long when there is so much to see elsewhere.

If you are in to hiking Gros Morne is amazing.

Also you could consider flying in to St Johns and doing hiking on the East Coast Trail
http://eastcoasttrail.ca/
You could drive up to Bonavista and Twillingate.

I'll assume you know what the flight options are. I would probably go with Deer Lake, if outdoors and hiking are your major interests, but I have some questions.
What are you expecting in Lark Harbour? There's a short but scenic hiking trail, but it is a tiny village. gros Morne Park in Bonne Bay is a large and varied region, with boat tours, trails, a variety of lodging options. With 10 days I would go up the Northern Peninsula and see L'anse aux Meadows.
If you fly into Gander, I would probably take the suggestion above to combine Twillingate with the Trinity/Bonavista area, with has a great variety of history and scenery and culture.
How did Springdale get on your list? I believe there are some high-end cottages nearby, but there aren't a lot of tourist activities, it's really just an average small town, with emphasis on small.
Finally, I'll repeat my standard advice: visit the government's tourism website at www.newfoundlandlabrador.com
Oh, and very crucial: reserve a rental car early!
Enjoy!

Thanks for all the info!

The rental car is reserved.

We finally opted for in and out from Deer Lake and will be concentrating one that section of the coast. We think we will fall in love with the province and will come back to explore another section in future years.

We chose Lark Harbour because we found a great rental by the sea. It will be our "relaxing" leg of the trip.

For the rest, Bonne Bay/Gros Morne it is! Can't wait!

Hi Jojonana, It looks like you made a lot of your choices already, but I had to agree with the comments on Lark Harbour. It is a beautiful drive from Corner Brook to LH, and the little trail up and around Bottle Cove is beautiful and you can find a good spot for a picnic. There is also some hiking in the Blowmedowns. BUT it really is just a nice day trip. I would suggest that you consider renting a cottage in Gros Morne instead. Woody Point is a beautiful quiet town with with rentals and you have Gros Morne NP as your playground. It is very quiet, peaceful, but with things to do. You can find a few restaurants there, listen to live music, go to presentations at the Discovery Center, take a boat tour of Bonne Bay, take a water taxi to Norris Point, or drive over to Trout River and take a zodiac tour behind the Tablelands.... You can fish off the town pier, and meet the locals. For hiking you have a choice of many trails both in and out of the park. Other small quiet towns in Gros Morne include Trout River and Norris Point. All are great places to stay but as you can tell Woody Point is my favorite. One of the reasons is how walkable it is. If you decide to stick with your plans, I am sure you will have a nice time, but may find yourself driving more than you planned if you want to eat out or go for a hike. Regardless, have a wonderful trip. Newfoundland is an amazing place.