Which is correct: "it's not a big deal to me" or "it's not a big deal for me"?

Either is acceptable. I would probably choose "for me", personally, but I would not think it strange to hear someone speak either form.

As for your second question, I would say that "It's no big deal for me" carries more emphasis on 'no' than "It's not a big deal for me." Both are equally acceptable, and the difference is very subtle (in fact, some people may disagree with me on that difference in the first place).


Also, you can use "not" or "no", but if you use "no", you need to omit the article, "a".

It's not a big deal. It's no big deal.