I found many examples for ～て初めて with positive verbs, for example:
生まれて初めて寿司を食べた。It is the first time in my life I ate sushi.
病気になって初めて健康の有り難さが分かってきた。I began to know the value of health only after I was ill.
Can ～て初めて be used with negative verbs? Are there any examples?
Is it correct to use ～て初めて as follows?
あの角を右へ曲がって初めて先生の家が見えます。The teacher's house will be visible only after you turn right at that corner.
Sure, you can use it with a negative predicate no problem: 生まれて初めておいしいケーキを見て食べたくならなかった。
For the second, in the case that you're giving someone directions or something, it doesn't sound wrong, but 初めて sounds like the first time ever. Maybe …曲がったところで、（やっと・やがて）先生の家が見えてくるはずなんです is better?
While Brandon's example about Cake shows a negative verb can be used with 初めて, I feel that in general that is an exception. I searched online and found a few other examples where a negative verb was used after 初めて:
20年目に初めてやらない年になってしまいました
Here, this means that this was the first year (after 20 years) where something wasn't done.
実際にいろいろ初めてやらないといけない仕事もあるので
This indicates that there is some jobs which you'll be doing for the first time.
はじめてしないで寝れました
This indicates that the person was able to sleep for the first time without doing something.
As you can see, in all of these cases there is some context where it makes sense to use a negative verb after はじめて. I can't think of any case where the simple form "初めて" + (negative of verb) would make sense, except Brandon's example with "食べたくならなかった". For example, this sentence seems strange to me.
僕は初めて見ない.
I think saying either of the below would be more natural.
僕は初めてじゃない。
僕は初めて見るわけじゃない。
僕は見たことがある。
Regarding the second question, I agree with what Brandon said, but here is one other way to express that.
あの角を右へ曲がったら先生の家が見えてきます。
Question: Can ～て初めて be used with negative verbs? Are there any examples?
I think you could use "negative verb + て初めて" (「～ないで初めて」「～なくて初めて」), as in:
「動いて当たり前と思っていた指先が動かないで初めてそのありがたみを知ったわけです。」
「その後もリバウンドしなくて初めてダイエットが成功したと言えるんです。」
but I have a feeling that this is not very common. I think it'd usually sound more natural to use 「～なくなって初めて」 , as in:
「体が動かなくなって、初めて健康のありがたさが分かった。」
Bonus question: Is it correct to use ～て初めて as follows?
あの角を右へ曲がって初めて先生の家が見えます。
Your sentence sounds fine to me. Compared to the normal 「あの角を右に曲がったら先生の家が見えます」, I think 「曲がって初めて～」 and 「曲がったところでやっと/ようやく～」 emphasize that you can't see the house until you turn the corner... This is the same thing as the English "If/When~~" vs "only after~~" "finally~~", maybe?
