I am not sure about which forms are correct.
That money is enough to donate to charity
That money is enough to donate it to charity
--
This car is very luxury to buy.
This car is very luxury to buy it.
Should we use a pronoun in the infinitive clause?
I think that the sentences without pronouns are correct.
Do you agree?
You are correct in your assumption that the pronouns ("it") are not needed.
That said, the sentences without the pronoun have some problems of their own.
Native speakers would not say:
This car is very luxury to buy.
but they might say:
This car is too luxurious to buy.
or perhaps even better:
This car is too luxurious to afford.
Rearranging the sentence completely, and using an idiomatic expression, a native might also say:
This car is out of my price range.
As for the second sentence:
That money is enough to donate to charity.
Let's say that money is 50 euros. It's not clear whether you are saying:
a. that you plan to donate the 50 euros (and you wouldn't make a donation any smaller than that), or
b. that you need, for example, 40 euros to get through the week; therefore, you now have enough extra that you can afford to donate 10 euros to charity
Either way, I think a more natural way to say it might be:
We have enough money that we can donate some to charity.
There is no requirement to use the pronoun it there but the pattern occurs frequently in speech.
The risk was enough to take seriously.
The risk was enough to take it seriously.
As you know, these alternatives (and quite a few others) exist:
It was risky enough to be taken seriously.
It was risky enough to take seriously.
P.S. The pronoun there is a colloquial usage. Should we avoid using the pronoun? In formal documents, the answer is probably yes.
