Personally in the sentence means individually. It's possible to meet someone as part of a group, or be introduced to someone where you don't have an opportunity to really talk to them, but meeting someone personally means you introduce yourself and have an initial conversation.
In person means not via the phone, Internet, etc.. It means you and the person you are meeting are physically in the same place.
If the young man has never seen the father at all yet, really the distinction above is not needed. So merely say:
I have not had the honor of meeting you yet, but I hope see you soon.
Otherwise use personally. Unless you've only talked on the phone to the father and are finally actually going to see the father face-to-face.
OK - my background is as a native British English speaker.
1) If I knew you were coming, I would've arrived from work earlier.
This is perfectly easy to understand, though as you correctly say, the grammar is not correct. "Had known" is really needed. Still, some native speakers will say this.
2) If I knew you would/were gonna come, I would've arrived from work earlier.
I find use of the contraction "gonna" the worst part of this construction. I think it may be more acceptable in American English. The same comment as above applies, of course, to the verb.
3) If I knew you had come, I would've arrived from work earlier.
This sounds unnatural and needs a slight pause in thought to understand. I'd suggest you avoid it.
To a British English speaker all of these constructions sound a little jarring, but in informal situations, native speakers commonly use constructions which are grammatically incorrect. There is a danger in formal situations, that a native (British) English listener will assess your level of education or ability, to be less than it really is, if you use constructions like this. That will also depend on factors like the age and background of the listener.
Incidentally, and again in British English, the contraction "I'd have" is probably more usually used, than "I would've" unless there is emphasis on the "would".
Best Answer
Sure, you can use unless in hypotheticals. Whether or not the situation has materialized has no bearing on whether or not you can use unless. Indeed, the purpose of unless is creating conditional clauses. Consider:
The constructions are ordered differently but have the same meaning; if one structure is transformed into the other, the semantics are preserved. In both cases, the statement says that B is a necessary condition for A; A is false if B is false, and B is true if A is true. However, saying that A is true if B is true a logical error. For example, your examples:
A (getting to the meeting on time) is false if B is false, because this sentence tells us the only way to get to the meeting on time was to catch an earlier train (which is if A then B). But catching an earlier train does not guarantee arriving at the meeting on time; what if I forgot my briefcase and had to go back?
Here, A is I should expect his help and B is he's my friend. This sentence says don't expect help from anyone who's not your friend (if not B, then not A). Note that just because he is your friend does not mean you should expect his help.
Notice that in sentence 2, B doesn't include not. Using not or not depends on the content of the sentence. Observe:
Here, B is logically not raining, because the statement means if we don't go to the park, it must be raining.
If A then B and if not B then not A do in fact have the same meaning. For A to be true, B must also be true allows us to deduce that if B is false, A must also be false. See Wikipedia for further explanation of the logic of implication.
But the discussion of predicate logic is beyond what you've asked. Simply put, it's perfectly OK to use unless for imaginary conditionals. As for the sample sentences, your use of unless is correct. They don't sound quite natural, but in both cases it's a matter of conjugation, not conditional clause structure. Here's how I'd change them: