Prepaid sim on unlocked or locked iphone11

I have an iphone 7 through Pre-paid and would like to get the iphone 11 through the Apple site since Prepaid is not offering the iphone 11.

Can i use the same sim card i have on my iphone 7?

When placing an order from Apple site, do i order the phone without a sim card or do i chose ATT as the carrier. 

It asks which do i want to do, but when I  sign into the ATT site it says I dont have an account.

"Prepaid ATT" is a different account/site and is the reason why I ask if I should order the new phone without the sim card. The phone will be unlocked since making a one time payment as well.

Do I place the sim card from my 7 into the 11 without choosing a carrier on Apple site? I guessing i dont have to have a carrier to buy the iphone 11. Inserting the sim card from my 7 will work just fine.