To answer your question:
1. Fine as is, or you could say "would ever make" (omitting the "have"). Both sound good to me. And "would" already is a modal verb.
2. Both are correct (As a general note, when you use the past participle tense ("had accepted") you're generally emphasizing that something in the past is now affecting the present. But the choice is up to you -- they sound equally natural.)
3. "in" NOT "at". The expression "in that time" is the same as "during" that time". Saying "at that time" means RIGHT NOW, AT THIS EXACT MOMENT.
4. Had become.
5. Both are correct.
6. Both are correct.
7. Both are correct, although I personally would choose "had offered" because it emphasizes that something that happened in the past is now affecting Julie and David's relationship in the present.
8. Regarding the question in #8 and #5, I believe that the simple past is used here because it's part of a conditional clause. So it's not that an action actually occured in the past, it's just that this is the sentence structure that is used in English (and many other languages) to express that this is a hypothetical situation ( ie conditional).
**Maybe so other members can explain better than I?
Best to you in your English endeavors!
In Perfect English