Can I 3D map with this drone? or am I limited to what the builtin screen has on it?
You need a standard Remote and a smart device. DJI’s built-in screens are not compatible with sdk apps, unfortunately.
You can pair it with a standalone Phantom 4 series remote and use a supported mobile device.
I can pair it with a standalone Phantom 4 series remote! Is this an easy thing to do? If I get a remote and supported mobile device and the right mapping app?
Yes! You can use a standard remote with the P4P+/P4A+. The aircraft is the same. Binding a remote is documented in the manual.
Thanks Dave ! 
Now Looking for remote.
Is their a buy and sell category on this site?
Do you own due diligence, but they can be found for less than $200.