Learn English – The difference between “would buy” and “would have bought”

In situation 1, which version you select (they're both grammatically correct) depends on the tense in which you're telling the story. If you're telling the story in the present tense ("So I'm walking along the street..."), you would use option A to match, while if you're telling it in the past tense ("So I was walking along the street..."), you'd use option B.

In situation 2, you'll generally want either A or C.

The essence of the grammar article was probably that in English, it's possible to discuss either past events or hypothetical future events in the present tense, as if you were placing yourself in the time and narrating from that perspective. In this case, you'd use the present-tense "first time I've been", but it's much more common to narrate this way when relating past events than when talking about future plans.

1: You wanted to do it means that at some point in the past you were willing to do it

3: You would do it means it isn't always something you are willing to do but you may do it if...

EDIT:

Want suggests desire, it implies that you are happy to do something, if you want something you'll take measures to get it (trade, buy, steal...)

• I want a pony, I'll go out and get one if I can.
• I wanted to go to London but something stopped me.
• I would want to go to Spain but I can't afford to.

Willing suggests that you will do something, but you might need to be persuaded or paid. It in no way means want.

• I am willing to look after a pony, but I'm not going to try to get one.
• I was willing to go to London but I had no reason to go.
• I would be willing to go to Spain with you if you want to go, otherwise I would not go.