kdavid,
You have a great goal, and you've taken some good steps towards achieving it.
Before I say anything, I'd like to say this:
The #1 most important part of your Chinese history phd application is to have a proven record of extensive research in the field of Chinese history, utilizing target-language primary sources.
I have walked a similar road as you, and I think there are a few things that I can help you with. The first few points could be called a rather harsh "reality check."
First: A masters in history at a Chinese university (even at Beida, the Harvard of China) is of little value, especially if the person earning the masters is a foreigner. This is not my personal opinion. This is straight out of the mouth of a well-known Princeton professor. What it will do for you is show that you have above-average Chinese language ability. What it will NOT do is make up for your lack of an undergrad Chinese history major. I would have to go into a lot of detail to prove this point, but in a nutshell: Chinese graduate school is very poor quality (although this is beginning to change in the areas of science and technology). I am serious when I say that top-10 Chinese history profs will view a masters from a Chinese university as a cop-out.
Second: Your English teaching experience, extensive though it may be, is also of little value. All 5-6 years of it is worth no more than a 1-sentence mention in your SoP. This is because teaching English is completely unrelated to the field of Chinese history. If you were applying to TESOL masters programs, you'd be set. But no history professor is going to be impressed by English teaching (and let's admit it, foreigners teaching English in China, even at a "professional" level, are a dime a dozen).
Third: At this point you may stop reading. But do continue on: I've had to learn all these things the hard way, and I'd rather you not have to. Here's the last "reality check" I have for you, before I start listing your 优点。I know exactly what it feels like to be a foreigner in China, especially a foreigner who speaks good Chinese. It feels really good. We get respect, compliments, friendships, job offers out the wazoo. After months or years of this, we start to believe that we really are spectacular -- unique -- even brilliant. (I'm sure you've been called a language 天赋 many times. Haven't we all.) And then when we come home to the US, people fawn all over us all over again. Wow, you've lived in China! Wow, you speak Chinese! You must be brilliant! So, to the average Chinese, and the average American, we are obviously Ivy League material. But the Ivy league profs and admissions committees, they can see through all the fluff and gloss. I'm not saying that you're NOT brilliant. I don't know you, I have no idea. But your plan for applying to an Ivy League PhD i can say with some assurance will not get you in.
Here's the good news.
First: Your preparations are quite likely to get you into an Ivy League masters program. Once there, you can 弥补 your research 不足, and apply to PhD programs again, this time with a great deal of confidence.
Second:I have spent years in China. I understand your drive (as perhaps normal Americans do not) to attend a 名校. And I completely support you in that. In the threads above, no one mentioned the fact that humanities PhDs are in oversupply. Even grads from top-tier schools have difficulty finding jobs. Advice given to me by a Yale prof: If you can't attend a top-10 program (I don't mean Ivy League-- I mean top 10 in CHinese history), don't attend at all.
Third: Cheers to your language prep! To round out your language skills, I'd definitely work on Japanese and Classical Chinese.
I hope that was helpful. Good luck! (And if you do get into an Ivy phd program, I'll be thrilled to death).
-- b