You can reach Halfhill by traveling to the west side of the Jade Forest. Take the road that leads due west from Serpent's Heart:
Continue to travel west on the road through Valley of the Four Winds until you reach Halfhill:
The first quest you pick up from Sungshin is "So You Want to be a Chef?". I'm still working to verify the floor on this, but so far the quest is available as low as 350 Cooking skill. It would appear that Sungshin's recipes are intended to help players power their Cooking skill to Zen level if needed. If you're not at 525 skill, go ahead and use Sungshin's recipes to skill up.
Once you reach 500 Cooking skill and complete the first quest, Sungshin offers the follow-up quest Ready for Greatness. You can't actually make the dish she's requesting until 520 skill. When you turn in this quest, she will teach you the Zen Cooking ability and give you your first Ironpaw Token. Completing this quest also unlocks the six specialization quests, what I like to call the "Way" quests.
Each "Way" quest is done one time and unlocks the specialty recipes on the corresponding Master trainer. Once you complete the "Way" quest from Sungshin, you return it to the appropriate Master trainer. He or she will then offer you a quest that grants you access to the specialty recipes and unlock the first one for you. Completing this quest will also get you a second Ironpaw Token. After that your specialty trainer will teach you additional recipes from his or her specialty. Simply continue to craft specialty recipes to level up your Cooking skill as well as your specialization skill.
Many of the Pandaria specialization recipes grant 5 skill points when first learned. This may sound great, but these recipes also require 2-10 components to make. Luckily you get multiples of the finished product. But once you reach the specialty feasts, you're looking at as many as 141 components to craft a 25-person feast. Yes, you did read that right, I said 141 components per large feast. Eventually Farms will help with some aspects of the collection process. But Panda Cooking looks to be very labor intensive, at least until supplies start trickling into the Auction House.
All "Way" quests can be done simultaneously, you can work on all six at once if you like. The main limiting factor here to unlocking all six specializations is the materials. Each pair of quests will typically require 10 of a specified ingredient (5 for the Master quest and 5 for the "Way" quest). Some of these ingredients may not even drop in the early zones, so getting your hands on them could be difficult. Eventually this won't be a problem as mats become available on the Auction House, but early on the mats will be in short supply. To make matters more difficult, the Agility and Strength specialties both require the same material (Raw Tiger Steak). So expect that item to be even harder to collect, with potential overfarming of tigers in addition to AH price gouging.
Luckily you can unlock any of the specializations and start leveling up. In MoP, your official Cooking skill is determined by your highest specialization skill. It won't necessarily help you unlock more specialty recipes, but at least you can work on your overall Cooking skill. The easiest specialty to start with is the Way of the Pot. It requires Jade Lungfish, which can be fished up in the very first zone (20% estimated drop rate).
Another option is the Way of the Oven, which requires Wildfowl Breast that drops from various birds in Pandaria. There are unaggressive cranes in several areas of the Jade Forest who drop them and are generally not quest targets. You can use these instead of Jade Lungfish if you prefer to hunt mobs. The cranes are a high drop rate and some are 100% drop, but there are not high numbers of them and some areas cannot support multiple farmers.
At 550 skill all of the 530 recipes become yellow, so you should learn the next recipe from your specialty trainer. I opted to stay with the Way of the Oven since a Twin Fish Platter requires 2 fish instead of 1 fish + 5 veggies like some of the other recipes. It took me over an hour to collect the 50 Krasarang Paddlefish needed to craft the platters, these fish have a 20% drop rate according to El.
When you get to 575 skill you can learn two new recipes: a great banquet that feeds 25 or a normal banquet for 10 people. Most of the 575 recipes require a combination of fish/meat/veggies and 1 vendor-bought item. Skill-ups are worth 5 points for the smaller feast and 8 points for the larger feast. The larger feasts requires twice the mats of the smaller feast, so you get more skill points from your mats by making the 10-man feast. You'll need to collect at least 50 meat + 50 fish + 250 veggies to make the banquets. Count on this step taking many hours of farming depending on the drop rate of your components. The 575 recipes will stay orange all the way to 600.
Eventually you'll be able to do a quest for Nam Ironpaw. He will offer you "Preserving Freshness", which simply requires you to purchase an item from Merchant Cheng a few steps away. This unlocks a repeatable quest which can't be done until level 90. Nam Ironpaw will accept a Bundle of Groceries as a repeatable turn-in. You can purchase empty containers from Merchant Cheng, which will allow you to exchange stacks of 100 veggies, 20 meat/fish or 60 Golden Carp for one Ironpaw Token. Tokens can then be used to buy sacks of Cooking ingredients. This essentially let's you exchange one type of item for another.
All of the quests at Halfhill reward Ironpaw tokens. Any SW/Org cooking tokens you already have will be converted to Epicurean tokens in MoP. The cooking dailies in SW/Org still reward skill points, so for now you're able to use the SW quest as an added bonus in the leveling process for MoP. You can also do the Darkmoon Faire Cooking quest for skill points if you like, although this won't be available at launch. Doing all of the specialty quests at Halfhill should get you a handful of Ironpaw tokens before you reach level 90 and unlock the daily quests. You will likely need to do all starter quests if you're trying to power level your Cooking skill, as it takes 1 Ironpaw token to purchase the vendor item 100 Year Soy Sauce, which is needed for banquet feasts.
Realm First Thoughts
At first glance Way of the Brew seems like the easiest specialization to start with since Sungshin sells the Ginseng needed for the first recipe. While this will help you in making the items, subsequent recipes are actually much worse on the Brew path. At 550 the "Brew" recipe calls for 10 vegetables while two other Ways are only requiring a couple of meat/fish. Then at 575 the "Brew" recipe takes 100 vegetables while other Ways need only 70 meat/fish/veggies. With Farms not in production yet, you'll have to collect all the veggies by killing mobs. Because of this, the Brew path will likely be the most time consuming.
Do extra "Way" quests from Sungshin to collect the additional tokens needed for feasts. You're going to need five 100 year soy sauce to craft the recipes at 575. The best way to get them is to do additional "Way" quests. The quests from Sungshin will not be enough to get all the Ironpaw tokens you need.
There are no longer any gotchas in the Cooking progression. It looks like Blizzard removed them at some point. The final set of feasts will stay at orange difficulty all the way to 600. The main challenge in capping Zen Cooking is collecting all the meat and veggies to make the recipes.
Feel free to ask questions in the Comments and I'll do my best to answer!