Port in two lines and a watch

Sorry for such basic questions - I have a current account with 2 lines on it.
I am wanting to port in 2 numbers (one is my wife's phone and one is my main line on my phone, the second line is already USMobile). I also want to port in my watch.

I see I can add a line, then it takes me to checkout but I do not want to checkout until I know I am doing it correctly.

After I check out, it will give me the option to port the numbers from the other carrier, correct?

And I should not be doing that until I am ready to port since the billing cycle start immediately, right?

Thanks for any info and insight.