A very thoughtful and hard question indeed; it pushed me to research a bit on the subject Continuous Conditional.
Your first example is a past perfect continuous sentence. In general, it is used to indicate an action was happening before another action happened. However, it can also be used to indicate past unreal condition. For example:
If I had been talking to him when he said that, I would have punched him in the face.
But fortunately, he was not talking to him when he said that and that's how he missed my punch.
So according to this theory, your first sentence which is
If I had been with you, I might be taking care.
is absolutely meaningful and grammatical.
Now, there is a vital fact when using these type of constructs as described by data.grammarbook.com,
When talking about something that didn’t happen in the past, many English speakers use the conditional perfect (if I would have done) when they should be using the past perfect (if I had done).
For example, you find out that your brother saw a movie yesterday. You would have liked to see it too, but you hadn’t known he was going. To express this, you can use an if – then clause. The correct way to say this is with the past perfect in the “if” clause, and the conditional perfect in the “then” clause:
Correct: If I had known that you were going to the movies, [then] I would have gone too.
The conditional perfect can only go in the “then” clause — it is grammatically incorrect to use the conditional perfect in the “if” clause:
Incorrect: If I would have known that you were going to the movies, I would have gone too.
More examples:
Correct: If I had gotten paid, we could have traveled together.
Incorrect: If I would have gotten paid, we could have traveled together.
Correct: If you had asked me, I could have helped you.
Incorrect: If you would have asked me, I could have helped you.
The same mistake occurs with the verb “wish.” You can’t use the conditional perfect when wishing something had happened; you again need the past perfect.
Correct: I wish I had known.
Incorrect: I wish I would have known.
Correct: I wish you had told me.
Incorrect: I wish you would have told me.
Correct: We wish they had been honest.
Incorrect: We wish they would have been honest.
So this theory, in a nutshell, says you can't use "would" part with the "if" clause, rather it should be used in the result clause. So, according to this theory, your second sentence stands incorrect.
They're all grammatical.
You could say
In those days, I was taking the train to work every day.
In those days, I took the train to work every day.
In those days, I would take the train to work every day.
The first, was taking, puts emphasis on the action as recurrent action, corroborating or reinforcing the meaning supplied by in those days and every day.
The second, took, relies solely primarily upon those temporal phrases for that meaning. (The simple present and simple past can refer to customary behavior.)
The third, would take, also corroborates and reinforces the idea of recurrent action, my then customary behavior.
The subtle difference between was taking and would take is that the continuous refers to the action as repeated or recurrent action, whereas would take refers to the single action as emblematic or representative of the customary behavior.
Best Answer
He was going for a morning walk every day.
He would go for a morning walk every day.
Both the sentences are grammatical, but there's a difference between their meanings.
The first sentence is in the past continuous. You can use this tense to refer to something that you did again and again in the past. The sentence means that he used to go for a morning walk again and again every day. The sentence is grammatical though it's odd or unusual. You usually go once, not several times, for a morning walk every day.
You can use would instead of "used to" to refer to something that you did regularly or habitually in the past. The sentence is quite clear. It was his habit or routine to go for a morning walk every day; of course, it conveys the sense of going for a walk once, not several times, every day.