そうです expressions

Question

I've been learning Japanese for a few years now but I still haven't fully grasped the ways そうです is used in conversation.

What I'm concerned with are the following expressions:

1. そうです/そうなんです
2. そうですか/そうなんですか
3. そうですね/そうなんですね
4. そうかな

I haven't found a thread that fully addresses what each of these mean/how they are different to each other etc.

If anyone could give me a hand I'd appreciate it so much!

Answer 1

なん　is, of course, a short for なの, and in the above examples does no more than strengthen the assertion of the speaker. (http://jisho.org/word/%E3%81%AA%E3%81%AE)

1. Both mean "that's right" or "that's correct".

2. Both mean "is that right?" or "is that correct?". But I'd say that depending on the tone in which they are spoken, they could both include either relief or disbelief (or even acceptance of what the speaker knew was going to happen, but that's a bit melodramatic) in whatever triggered their being spoken in the first place. Note that my only source for this is anime and games, and the way the characters in them decide to express themselves.

3. Both mean "that's right, isn't it?" ("isn't it?" being rhetoric of course). Depending on how they are said, they could mean "I guess so(.../!)" with a trace of, again, relief or disbelief.

4. "I wonder if that's correct/true..." http://jisho.org/word/%E3%81%8B%E3%81%AA