Raymond,
I like the iPad Mini. I personally use the Mini and the iPad w/ Retina. I have noticed the Retina displays draw more power and seem to overheat more in the heat of the summer, keep in mind I'm in Texas and this might not be a problem for you.
If you get an iPad that has Wi-Fi only, you will need a external GPS device like the Dual XGPS 150 or 160. We just set up as a dealer and should have these in stock shortly. My Pilot Store also has them. The Garmin Glo is also a nice one, but hard for get behind a direct competitor and I have one, disappointed about the battery and indicator light.
Additionally, if you are looking to move into the world of ADS-B, keep in mind most of these device Dual, SkyGaurdTWX, iLevil, Clarity all have GPS receivers in them, so you could use that GPS signal.
Wi-Fi + Cellular should provide you with a decent signal, however it is pretty widely discussed on the internet that he iPad GPS is OK, not great. you'd definitely experience better signal and accuracy with and external. I guess it just depends on your use and need.