No, you upgrade the dumb-phone line to a 5 with a 2GB data plan and then switch the phone to your line after you receive it. Then you can cancel the data plan on the dumb-phone line since it can't use it.
It sounds like you'll be fine with a 2GB plan if you don't want to do that. LTE doesn't use more data, but it loads content faster so you might visit more web pages, which is more usage.