The National Payments Corporation of India (NPCI) guards your data to be stolen as NPCI implements robust security standards to ensure the safety of digital transactions, by providing three-factor authentication, encrypted transactions, and access control, which makes it safe for use. So you can simply use the BHIM app to pay your bills.

You only need to register for GST if you are earning more than 20 lakh rupees. Since you are making less money than 20 lakhs, you do not need to register for GST.

Go with the HDFC Diners Club credit card:

It is a reward card that you can redeem while booking flights and hotel stays (upto 10X rewards).

Provides national and international lounge access.

Provides travel insurance coverage.

Experience amazing dining benefits.

As you mentioned, you are earning well, so you can easily get the high credit card limits. As credit card limits mostly depend on your income.