Any ideas on which one would be the best?

Wifi and 3g because I need the GPS available (dont know why its not standard, all android devices have one fitted)
Videos and photos would stay with the camera so I dont need much storage
What about the processers, any problems with add on software (Airnest, Litchi or Autopilot)
Which is the best for visibility, do I need to get a sun hood
UK so lots of options from refurbished to new ones

Any suggestions appriciated

Thank you

I would go with mini 3 64gb.
Yes, you need a sun hood to see it better.

The iPad mini 2 & 3 are basically the same, only difference is the 3 has fingerprint recognition.   The iPad mini 4 is faster and the screen is better as it's less reflective and easier to see outdoors.  I used my mini 2 to start with which worked fine but was hard to see outdoors so decided to get the mini 4 and noticed a difference straight away.  

Sunny1975lucky Posted at 2016-4-22 23:20
The iPad mini 2 & 3 are basically the same, only difference is the 3 has fingerprint recognition.    ...

Yes.Because of the A8 chip, mini 4's performance is higher than mini2 and 3.

Maybe  a mini 2, cheaper to start with, I dont need all the bells and whistles as it will only get used with the P4, I'm an Android man normally but some of the apps are only IOS

I've a mini 2 only wi-fi 16GB and it work good. I use this iPad almost only for pilot the Phantom, I think that if you want some iOS device that is cheeper, a mini 2 is good enough.

Been offered a mini 4 64gb, no 3g for 250gbp, 6 months old. I could get a seperate gps later

I ended up with the mini 2 16gb wifi/3G from eBay, turned out to be 32gb and unlocked so was a bargain for 170gbp