-Estimated achievement difficulty: 4/10
-Offline: 11 (Plus 3 DLC)
-Online: 1 - Warlord
-Approximate amount of time to 200: 10 - 12 hours
-Minimum number of playthroughs needed: 1
-Number of missable achievements: None!
-Glitched achievements: None!
-Do cheat codes disable achievements? No Cheats
-Does difficulty affect achievements? No!
While I put the difficulty at 4, the 'Master Craftsman' achievement would stand at about 5/6. I just rounded down because of the ease of the others. There are no missable achievements in this game.
I suggest playing on the 'Normal' difficulty until you get to Sartek and then switching to 'Easy'. This way, you'll fly through the final parts of the game. You can continue with side quests and other achievements after the story has ended.
After completing story you will have at least 7 out of 12 achievements so that's those out the way!
Warlord Achievement - Very easily obtained, just go here and ask for someone to let you win or contact someone willing to trade.
Legendary Hero Achievement - Check this thread. Extremely easy to level up in this game, also following the instructions in the thread allows you to get enough gold to fully upgrade your Citadel for the "Master Engineer" achievement so don't worry about spending your gold on items.
Beast Tamer Achievement - I didn't get this until near the end of the game where the puzzles are so much more difficult than at the start so I recommend using this solution guide, even at the start if you're unfamiliar with the concept.
Knowledgeable Hero Achievement - Wait until the end has been and gone, then backtrack all the way to the first area to fight the easiest/weakest for this, should only take 1 or 2 tries, you have to collect the scrolls in the puzzle the same way you would with the skulls, gems etc.
Inspiring Leader Achievement - There is a post containing the location of all companions here.
Master Craftsman Achievement - This is the most annoying task in the game, you have to try and match up 15 anvils to each other (not all at once) by breaking gems to allow the anvils to fall into place. Much like the way to get Spells from enemies. It took me 15+ attempts over 2 days. The runes you'll need to craft are:
Rune of Axes (Base Rune - Weapon)
Location: Blackhoof, Realm of War.
Rune of Poison (Power Rune)
Location: Snake Fang, Down near the trolls/ogres.
Rune of Gods (God Rune)
Location: Valley of Kings, Center of the country.
The best mindset to begin this achievement is "This is just a practice go, I might get it next time!", just so you don't get too disheartened when you fail. But in all seriousness, you might get it first time. It all depends on luck and where the anvils appear/fall.
After reading this, you should have an idea of what you need to do for certain achievements or what you need. All round, pretty simple achievements bar one and you've had the satisfaction of clearing one of the best Arcade games around!
[x360a would like to thank chrisnottm for this Road Map]