1. I'm sorry, it should be 心の支えっていうかさ, as you say. So, 支え is a noun and って is quoting, right?
3. Yes, the first っ is there, but of course it could be a typo in the book.
4. I understand 「俺の生きがいは・・・」なんて考えてるところ(=こ と), but I do not understand the overall sentence structure, nor the が ... が pattern in your expanded version, nor the exact relevance of 優秀な証拠 in this context. I'm trying to make it mean that 「俺の生きがいは・・・」なんて考えてるところ is proof of the other person's good qualities, or something like that, but I cannot see how it works.