Hi I came across this sentence along with it's correction:

Wrong: Such persons who are diligent, achieve success in life.
Right: Such persons as are diligient, achieve success in life.

This raises three questions:

1) When adding "s" to person, when do we use people and when do we use "persons"?
2) Why is "as" better than "who"?
3) What does "as are diligent" actually mean? I mean, essentially it's trying to say diligent people, but the word combination sounds a bit awkward, unless of course, people from other countries say it and i'm just not used to hearing it said this way.

Would appreciate any feedback!
It's should read its.
No comma after diligent in the 2 sentences.

1-- Persons is primarily reserved for bureaucratic and legal use.
2-- Such...as is the correct idiom.
3-- I suppose there is an elision: Such people as [those who] are diligent....
ahhh, ok got it.