There are several English translation questions that I don’t know

In favor of is a prepositional phrase that cannot be used as a predicate alone and is often used together with be. So it should be:

I am sure I will be in favor of your decision.

There is only one action here, which cannot be compared, so it can only be in the past tense, because the past perfect tense is in the past past. tell sb to do sth has a fixed structure, so only prototypes can be used.