Can't decide which iPad Version to purchase

I'm planning to buy an iPad Air 2 and there are some questions in my mind. So far asking from other people hasn't help me so I came here to ask.

Before posting the question, let's clarify that I need some help regarding to some features of the iPads and I should mention the storage which suits me best is 64GB so my choices are iPad Air 2 64GB Wifi or iPad Air 2 64GB 4G.

-- Is there a speed difference in General usage between 4G and Wi-Fi model?

-- Do I miss much if I purchase Wifi Model since that saves me some money?

-- Does SmartCase from iPad Air First Generation fits in the new iPad Air 2?

-- Do I need a screen protector and does it's screen scratch?

-- Does Long-Charge technique still apply for these new devices or should I just use it like any other devices and charge it when it's needed?

-- Can I trust 3rd Party App Stores?

-- Do Apps use GPS a lot? if they do then how does the WiFi model manages location positioning?

-- Can I share my Android Phone's GPS using to provide location service for the iPad Wifi?

That's it.