Can I set up an iPhone for a child before adding cell service?

My child currently has another type of phone geared towards younger kids. We're moving her to an iPhone for her birthday this year, and we have an iPhone for this purpose already. I don't want to activate her phone number to the iPhone until after her birthday, but I'd like to do some basic set up on the iPhone now so when she opens it, it has her account set up already with apps, and is usuable on wifi.

My question is if I set the phone up NOW (create a child's account and an Apple ID and so on), customize the settings, and add apps, does anything change when I go to move her phone number onto this phone? Will I need to factory reset in order to add cell service? I don't want to spend a ton of time customizing it if I will need to factory reset.

Thanks for all the help.