Due to my presbyopia I would like to run Gaia on my 10" tablet and teather both my phone's cellular internet and GPS location to the tablet which has neither.
I'm probably within my monthly wireless hotspot allowance so the remaining question is sharing thr GPS location.
In the future if I would switch to USB tethering which Verizon can't detect (lik PdaNet) is there a cable that allows data between phone and tablet while charging both?  I suppose I could just use a powered hub.

Sure until you run out of signal, although most android tablets have stand alone gps even without a sim card in them.
I hot spot my phone and my Inreach mini to a tablet, With the tablet connected to the Inreach I can also use the tablet or phone to type messages instead of the clunky shit in the Inreach.

Be sure to download any and all maps that you want to the tablet before your cellular signal is unavailable.

Probaly not an app that shares another devices location and spoofs it to another device. but you maybe could spoof your tablets location data to wherever you want.

Not sure if this still works or not. or with a non gps tablet..  but give it a shot.

https://play.google.com/store/apps/details?id=com.rosteam.gpsemulator&hl=en_US&gl=US
Attached File

I have sucessfully added an NMEA client to my tablet.  I'm usung Bluetooth GNSS and it seems quite good.  For the server end on my phone I'm using ShareGPS 0.2.0 from 2010 after finding an apk and it is working.  0.3.0 and 0.4.1 were released in 2015 but have been removed from play store at some point.  The project page which has no activity since 2016 does not have the apk files.

I am now seeing the phone's GPS signal on the tablet in all aps!

I'm stll looking for a better NMEA server for the phone side.

PS. Just to be clear the tablet does not have a GPS receiver (or any cellular capability).