Help needed in deciding which products to list

I am a new seller registered with Amazon. I have my brand approved. However the brand approval was under children book category (education domain).

I haven’t added any products yet on seller central. I have got software solution to practice for entrance exams (Under same brand but for different age group / target audience).

My questions are:

1. Can I publish a product under same brand for which my brand was not approved?

2. I want to sell it as subscription, how does that work with amazon? any experience?

3. I should go for ads from day 1?