"You have to get your suitcase ready now."
Translation:Il faut préparer ta valise maintenant.
The differences between "falloir" and "devoir" is a subject for linguistic philosophers.
"Il faut" implies that something is necessary (necessary to have or necessary to do).
"Tu dois" implies that you are obliged to do something or you owe something.
Some sources online maintain that "Falloir" is stronger and more formal than "devoir", but from what I can see from the comments from native French speakers they are practically interchangeable.
The only marked difference between the two is that, because "falloir" is an impersonal verb, using "devoir" puts more of an emphasis on the subject of the sentence, and, conversely, using "falloir" stresses the thing that it is necessary to have or to do. But, in most contexts, that difference is minimal.
And for this sentence in particular, I think your translation should work, but, from what I can see, "faire ta valise" would be the way it is more commonly said.
Il faut + infinitive = "to need to [do something]" OR "must / to have to [do something]"
Falloir is only ever conjugated in the masculine 3rd person singular and here il is impersonal - it does not mean "he".
As the given sentence specifies ta valise → "your suitcase", it is clear who the sentence addresses. When a sentence does not provide extra information, such as "You have to go now" you can add specificity to it by adding an indirect object pronoun → "Il te faut y aller maintenant ".
NB In French, you can't say "go" without giving at least a hint of "where". "Y"stands for "là" or "là-bas" ("there" or "over there") either because the place was mentioned before or just to mean you are going somewhere.
To read more about the use of il faut see: here
"Il faut" can be, and often is, used without the extra pronoun. You're right though, the sentence "Il faut préparer ta valise maintenant" could be translated to "We need to", "You need to" or even "I need to" in English...
...but that is how the phrase is often used in the French. You can stress that "you" are going to be the one packing "your suitcase" with "Il te faut", but the French sentence is usually more about what needs to be done and not who is going to be doing it. If the English context were "You need to get your suitcase ready! I'm not going to do it." Then, if "il faut" were used at all, it would probably be "Il te faut".
That said, "Il te faut préparer ta valise maintenant." should be an accepted answer to this translation. It's just not the only acceptable and, arguably by some, it is not the most likely translation.
Thanks. I know it's common to focus on the action in such cases, and that English doesn't really have this sort of "il faut on doit" construct. Still, it was a bit odd to see this choice of words, as they portray a slightly different picture - one would be "C'mon, your suitcase won't get ready by itself" and the other is more like "You know you have to pack your stuff, right?"
I'm not sure about my preference is the context of learning a language - Normally, such grammatical nuances between literal meaning and common use would be explained as a side-note, but this platform does not have them, and in such case maybe it's better to stick with the more restrictive wording.