FNB credit card perks and interest rates

Ive been banking with FNB for about 10 years, A few years ago FNB called to offer me a credit card, I must have agreed because the credit card showed up in my internet banking. To date, I have not received the physical card and it was never activated, this never bothered me because I never needed the credit facility and I still don't.

To digress quickly, I have never bought anything on credit and the whole credit scoring thing never bothered me. I dont foresee myself ever needing to finance anything.

I only reason why I am even considering the credit card is that If I travel, I can't hire a car without a credit card.

So about two weeks ago I was in a hurry to transfer money, in the rush of the moment I used my banking app on my cellphone and by mistake, I transferred money to the credit (which I don't have access too).
When I tried reversing the transaction or re-transferring it back to my savings account the transaction was denied.

I contacted FNB credit card department for them to assist in getting the money back which they did quite easily, this is when they informed me that I could activate the credit card if I wanted too.

The consultant said she would get a private banker to call me with more information.

I just spoke to the private banker and they seem to be ready to activate the credit card, shes emailed me an agreement which I need to sign and mail back to them, what i need information on is this:

• The credit card seems to have a 20.75% interest rate, Is this interest rate not high?
• Are there any real advantages to me upgrading from a gold cheque account to a private cheque account, the perks of free lounge access and Ebucks isn't enough to sell me.
• If I do accept the credit card, how should I use and manage it effectively?