iPad with no cellular chip means no internal GPS. Having an external GPS does it all for you. But consider the cost of the external GPS is about the same as the difference between an iPad with and without the cellular chip and it becomes a wash in my opinion. You do not have to activate the cellular service for the GPS to work. So, once you buy the iPad, it cost you no more than an iPad without the cellular service. All of the functions on Foreflight used in the air only need the GPS and nothing else.
Just to be clear, you do not have to activate the cellular service on your cellular-capable iPad to use its GPS. I never have. Just get the cellular-capable iPad and that’s that. If you ever need to / want to activate its cellular capability, you can always do so on-the-fly, but you never need to do that to use the GPS.
I had never activated my iPad cellular service either. But recently my home Internet was out for two days and I faced the prospect of no COPA in the evening. Horrors!
I found the process easy and cheap. The iPad will connect to let you subscribe, even though you have no cell service. I chose the smallest option – IIRC it was 250MB for 24 hours, no automatic renewal. $5.00 all-in cost. Fast, too. I don’t plan on buying any kind of “plan” for the iPad but is nice to know it is so easy and quick and cheap if I ever need it again. I have an AT&T iPad Air. I don’t know if other providers differ much.