Is the expression "shoot low aim high" used commonly?

Could you tell me the meaning of "front and back"?

The idiom "know something front and back" means to be an expert on something or to study something and have complete knowledge of it. This idiom comes from the original expression which is to "know something backwards and forwards". This expression is perhaps more common to use than "front and back". Ex: She's read the book so many times, she knows it backwards and forwards. Ex: He knows cars front and back.

When's "must be" used?

"Must be" is used when you're expressing a thought or opinion that is very likely to be true. Here it's used when the person guesses who the person is, usually based on the information they have from another person or the context. Ex: A: It must be midnight by now. What time is it? B: Five minutes to twelve. You were right! Ex: You must be Charlotte! Jake told me so much about you.

Even if some words may have the same meanings, sometimes the word has more dramatic nuance compared to the others. In this case, does Rick say "the entire" because it has a stronger nuance than "all of the"?

Yes, that's right! It does have a much more dramatic effect saying "entire" instead of "all of the". Ex: My entire family is against me moving away. = All my family members are against me moving away. Ex: The entire world won't know what you're thinking unless you say it!

What does "so far" mean?

"So far" describes the conditions or state of something up until the present point in time. In this case, "so far" refers to the score of germs and people up until now in time. However, this video is a few years old, so this score refers to the time before the coronavirus outbreak. Here's some examples of "so far": Ex: So far, it hasn't rained today. Ex: I am not hungry so far but I will be soon. Ex: I still have a lot of packing to do for the trip. So far, I've only packed my clothes.

Can I say "The first team that answers the most questions" instead of "The first team to answer the most questions"? Do "that" and "to" have the same role?

Yes, you can say "The first team that answers the most questions" instead of "The first team to answer the most questions". "To answer" and "that answers" have the same meaning in this context.