French language Q&A Forum

I got this question:

Cette pomme est bonne. - Oui, c'est _______.

I answered bon because I knew to use the masculine, but my question is why it's c'est in this case. I've read the relevant pages ("C'est" vs "Il/Elle est" to say it is/she is/he is in French and Standalone adjectives after c'est are always masculine) and my interpretation is that this would fall under 2b of "C'est" vs "Il/Elle est" to say it is/she is/he is in French: 

I translated "how many times" (I've got lost) as "combien de fois" rather than "le nombre de fois".  This was not listed as an alternative, but according to my Reverso app they are both acceptable in this context.  When would you use one rather than the other?

Can you please explain the difference between 

Qui est ce qui

Qui est ce que

When I was small, I played with my Lego.

Can I check why L'imparfait should be used? I understand that l'imparfait is used for repeated actions or habit in the past. However, the English translation doesn't seem to reflect that. 

Within the context itself, I can argue that

1 - When I was young, I used to play with my Lego (as a habit) - Quand j'étais petit, je jouais avec mes legos.

2 - When I was young, I played with my Lego (one off event, which ended in the past) - Quand j'étais petit, j'ai joué avec mes legos.