Learn English – “Who said it best” is correct

The "correct" preposition is just a matter of idiomatic usage...

We ask a question of someone we hope may answer it.

We put or pose a question to that person.

We also sometimes direct a question at someone, but that wouldn't really work in OP's context. It's far less common overall, and tends to be used in respect of a single question (or single series of questions).

It's worth pointing out that all the above variants involving prepositions are relatively uncommon compared to the simple version - normally, we just ask someone a question.

The sentence is grammatically correct, and its meaning is clear. The usage of "which in turn" is fine.

Basically, the sentence has three clauses.

Money can be exchanged for goods or services [ that fulfill people’s needs and wants ] [ which in turn bring happiness ].

a) Money can be exchanged for goods or services.
b) (that = Goods or services) fulfill people’s needs and wants.
c) (which = Such goods or services) in turn bring happiness.

The phase in turn is used in the sense of "it follows that" (or "as a result of things in the series of events"). In a sense, you can think of "in turn" as something that describes events that each of them takes turn to happen. Here is its definition by Macmillan:

in turn
1 one after the other in an order that has been agreed or officially decided
  We look at each element of the process in turn.

2 as a result of something that is part of a connected series of events
  The oil-producing nations have decreased production, and this decision in turn has caused heating oil prices to rise in the United States.
  Her mother taught her, and she in turn taught her own daughter.