1,2,3. Your formulation is fine. It depends on the student's level, of course. I wouldn't burden a beginner with the fine points of tense usage in dependent clauses. Your formulation does leave out, however, the parallel formulation for the past tenses, including the conditional (with "would" instead of "will"). And it does leave out the case where the main clause is an imperative.

4. Yes, it took me quite a while to stop using the present when I said in Italian or French: I'll let you know when I'm ready. vs. (Fr, It) when I will be ready. And I'm quite aware of the French and Italian problem in changing the pattern going in the other direction. Spanish uses the present subjunctive in these cases, but even there I notice some (unexpected) "when I will be ready" types of usage.

5. Yes, I left out the cases of "forbidden future" in relative clauses, but you are right.

6. "because I will": "because" does not prohibit the future or conditional. I've never tried to list every single adverbial conjunction that triggers the "forbidden future" rule. Maybe there's a list somewhere. After finding it and studying it, you might be able to see a pattern worth telling us here on the forum!

7. Aside from the exceptions I cited with "before ... will", no, I can't think of any others. In American English "shall" is seldom used, so I'm not the person to ask about "shall"!

What does "My heart is in the coffin" mean?

Concerning "if you will pardon me", yes, yes, yes, I completely agree with you. It is the volitional "will".

I must say, the quote from Bill S. was an exceptionally clever one! And coffee sounds good just now!

I'll tell you when he arrives = I have something to tell you, I also want him to hear the news, so I'll tell you when he is here. I'll tell you when he will arrive = He will arrive here at some point, and I'll let you know of his being here at that exact moment.

The first makes sense. But the second paraphrase would also expressed with "I'll tell you when he arrives", so you haven't completely understood, I think.

In both cases the "telling" is fixed in time by the meaning of the "when" clause. His arrival triggers the telling. So either is a possible paraphrase of "I'll tell you when he arrives."

Now, as for "I'll tell you when he will arrive": This would not normally be used for either of the meanings you paraphrased above. In this case I take "when he will arrive" as a piece of information, the mention of some hour of the day, for example. It says "I will inform you of the hour of his (yet to occur) arrival." And it doesn't actually say when the informing will take place!!! Nevertheless you could add that: "I will tell you later when he will arrive".

Combining the two, I can say (albeit on a rare occasion!),

"I'll tell you when he will arrive when you sit down and listen"

which says, "At the time you sit down and listen I will tell you a piece of information, namely, the hour of his arrival". The sitting-down-and-listening-time triggers the telling, not his arrival time.

To complicate matters, the 'piece of information' idea is also possible in "I'll tell you when he arrives", which can also mean "I will inform you of the hour of his arrival".

So "I'll tell you when he arrives" is ambiguous.
"I'll tell you when he will arrive" is, in my opinion, not so ambiguous, since I only sense the 'piece of information' meaning here, not the 'trigger time' meaning. In English we just don't use the future tense in a when clause when we want the 'trigger time' meaning.

CJ