Double questions

English as a Second Language English Vocabulary, Grammar and Idioms
1

Fortunately in the morning the sea was so calm that they hade some time to relax.

Question ¹ 1:

After [i]Fortunately[/i] is a comma needed?

Question ¹ 2:

(1) silent
(2) quiet

Which one can be the best alternative to the underlined word?

 Thanks in advance.
2

  1. Yes,

  2. Neither word is a great substitute for ‘calm’, though ‘quiet’ is the only one that could be considered an alternative. If I were to substitute a word, it would be ‘still’.

3

Above all, thank you for the excellent answers!

(1)
   (a) If I [b]were to substitute[/b] a word, it would..
   (b) If I [b]substituted[/b] a word, it would...

   Are (a) and (b) equal?

 (2) 

      (a) ....'quiet' is the only one that could be considered [b]as[/b] an alternative.
      (b) ... 'quiet' is the only one that could be regarded as an alternative.

        Which one is correct?