Which credit card should I get as a first-time user?

On the add-on card: yes, the primary cardholder is fully liable for all spends on the add-on. There is no separate credit limit or statement. So only issue it to someone you trust absolutely — spouse, parents. Not friends, not siblings you have money disputes with.

The customer care experience matters more than people think. I've had two cards with similar rewards, and the one from the bank with better support saved me ₹18,000 when there was a merchant dispute. Don't underestimate this.