Asselama, Hela! Where are you from in Tunisia? I taught English in Sousse several years ago, and worked with some wonderful colleagues!
Your verbs are almost 100% correct. Here are the only ones I could find to comment on:
4 - Yes, both possible (I think - we Americans don't use shall)
7 - Shall doesn't work here; your other answer is correct
12 - Your answer works, but will have been traveling is better.
13 - Not would; may or might are better.
I think that's all! And your prepositions are also correct (by/for). By in this case means "not later than".
- For Teachers