I don't thing they are interchangeable. "Jibun" refers to the TOPIC of the sentence. That could be "me", "you", or just about anything. 彼、自分の車を使う。= he uses his own car. 自分の車ですか？ = is that your own car?

Basically they are exchangeable with each other. Of course, there are some exceptions. Could you give my some situations you are considering so that I can give you more specific answers. I don't understand the meaning of the second question. Do you want to know how to say you in japanese? Then, the answer is anata.

ほんとうーにありがとう、みなーさん！！＾＾

I guess not, it means my, or myself(oneself,him/her/on -seself. While watashi is I