Hi, so if I buy an iPad , do I need to get one with just wifi or wifi and cellular ? . Thanks

First look here to make sure you are getting the correct iPad...  http://www.phantomhelp.com/tips/best-tabletsphones-for-dji-go.18

I use an iPad mini 4 WiFi, but I connect the WiFi to a mobile hotspot. I think most will say get cellular, but if your phone has hotspot available you can connect the iPad to that as well.  I'm not sure how to explain it but without data there is something about the maps and being able to fly (someone will explain it better I am sure).  But if you connect your iPad to home WiFi, make sure you in the settings you have the maps set to Cache Maps.

WIFI only is enough. Make sure a minimum of MINI4 to keep up with the GO4 app. I always fly in Airplane mode anyhow!

Either is ok, here is a recommended device list for your reference.

Thanks for the info

If you get an iPad with cellular capability, does it need to have a SIM card installed or will the cellular circuitry be enough to light up the GPS module?  I ask as I have found a decent iPad Mini 4 WiFi+Cellular at a good price but the seller is not providing a SIM card with it (top right of screen says "No SIM").

Thanks!
C