I don't find the use of prior redundant at all in such circumstances. And appointments aren't "always" made in advance. Consider this dialog:
I would like to see the chief minister, please.
I'm sorry, but you need to have an appointment to meet the chief minister.
Oh, okay. Can I make an appointment right now?
No, I'm not the person who schedules the appointments.
If the person had answered by saying prior appointment, that would have clued me in that the appointment should have been made in advance, and that walk-in appointments weren't granted.
I think the answers by Peter and Mohit Wadhwa might reflect what I see. I don't think either sentence in the question is wrong. To me, the difference is more of a nuance that makes the second a better fit.
People would understand or figure out the intent of the first sentence from the context. But it sounds a little off to my native ear because it is unnecessarily ambiguous and it would be more natural to just use more precise wording; words more typically associated with the situation.
"Clothing" is a collection of individual items and isn't usually the word of choice if you are talking about a coordinated outfit.
"Appropriate" has many possible contexts, even in association with a job interview, especially if you are referring to a collection of items rather than an outfit. For example, dressing in consideration of the weather, the amount of coverage in terms of modesty, clothing and shoes that facilitate activity if the interview might involve extensive walking or other exertion, etc.
An appropriate "outfit" or "attire", on the other hand, goes to the appearance and coordination of the items; how they look together. Either of those terms wouldn't preclude consideration of the weather, modesty, movement, or other characteristics, but the focus would be on "looking the part" or "dressing for success", which would be the intended meaning.
Best Answer
It's important to understand why the test says "fortunate enough" is redundant in this context. The given sentence isn't saying that being fortunate is a required condition to own a house in the city, but rather a characteristic of those who do. We can rephrase the example as:
The problem is that, even though it's slightly redundant, it's perfectly natural to express this using "fortunate enough", because there is little significant difference between:
and
One says they are sufficiently fortunate, and the other says they are just fortunate.
It's "a difference that makes no difference". But many non-native tests of English like to "split hairs" to hide the fact that the test makers care more about students' ability to memorize trivia than to their ability to learn how English is actually spoken.