Activate Iphone

You would have to verify that with your carrier. Most carriers do the activation once you have received the device. You can activate it once you get it. Do you currently have a phone with that carrier, and are you going to be using the current phone number you have?

No. And you need the new phone with SIM for carrier activation.

Yes ... at least until your new iPhone is activated.

(I assume "prepare for activation" means you are telling the seller your telephone number that is to be transferred to the new iPhone.)

You will be able to use the current phone and then activate the new one when you get it. No problems.