This game took me just a little under 9 hours of game time to beat. For the fastest way to get all of the achievements, when you are doing the story mode, get the "Own the Mountain" requirements, it will save you time and you wont have to worry about picking them up between media callouts and other challenges.
When you get to the Lesser Snow God and Supreme Snow God, you should have at least half of the challenges done already from the story requiring you to do them.
After you finish the story, work your way up the list of mountains starting at DC Mountain Lab. These challenges are by far the hardest out of all of them because they are on a much more difficult setting, therefor, you want to get them out of the way.
As for the Kitty Cleanups and Magic Circles, do the routes a couple of times before actually attempting it fully, you will understand what you need to do and get the timing on the jumps down for it before hand. I found myself near the end of the game getting 500,000+ combos on the Magic Circles Challenges.
Another tip for the Kitty Cleanups, the different glitters are in sets of 10, and the last set is usually the easiest to get because the last piece of glitter you need to pick up counts as more then one to round out however many were missing in a set. I found myself getting around 95% of the challenge actually doing it, then just picking up the last one and finishing it out.
The hardest challenge I had though was the Rail Call out on Zugspite about halfway down. It took me about an hour just to get a gold on this stupid call out.
Another tip for this game, if your challenges are halfway down the mountain, instead of taking the midway lift and snowboarding/snowmobiling down the mountain, take the top lift and use the hang glider, you can get moving a lot faster, then drop off right above the challenge, hit the b button, and switch back to snowboard and be ready to do it. This tactic saved me a lot of time.
As for the snowmobiling merit badge, you should pick this up around 3/4 through the story, and the park builder all you have to do is make the same item 10 times, delete them all, rinse and repeat. The sledding one you will pick up from the challenges as well, unless you suck at falling, which is like failing at failing.
Good Luck getting 1000/1000
It's not that hard, just got do things in the right order.