Learn Farsi: او یک ورزشکار بسیار ماهر است، اما از هوای سرد می‌ترسد. - He is a very skilled athlete, but he is afraid of cold weather.

To express "No matter how skilled an athlete he is, he is afraid of cold weather," you drop اما and change the first verb to the present subjunctive: هر چقدر هم که ورزشکار بسیار ماهری باشد، از هوای سرد می‌ترسد. The phrase هر چقدر هم که triggers the subjunctive باشد instead of the indicative است.

Why do we use از before هوای سرد instead of just pointing directly to the cold weather?

In Farsi, the verb ترسیدن (to fear / to be afraid) requires the preposition از (from). You aren't afraid "of" something in Farsi; you are afraid "from" it. So, از هوای سرد می‌ترسد literally means "he fears from the cold weather."

In the phrase یک ورزشکار بسیار ماهر, where exactly does the ezafe vowel go?

The ezafe attaches to the noun ورزشکار (athlete), making it pronounced as varzeshkar-e besyar maher. The word بسیار (very) is an adverb modifying the adjective ماهر (skilled). Because they act as a single descriptive block, you only need one ezafe linking the noun to the entire phrase. You do not put an ezafe after بسیار.

Could we use the indefinite suffix ی instead of the word یک here?