You can use the iPad to take calls as long as you have a phone and they are both on the same WiFi, so no not as a stand alone phone, take a look at the 7+ as it is larger than the small phones and not too far off an iPad mini
That depends on how much you need or want a new iPhone with updated features and capabilities. There will always be a new and improved iPhone coming along so at some point you have to decide not to wait for the next generation iPhone and buy what's available right now. If you're always waiting for the latest, you'll end up never buying.I have a 6+ now anyhow I just ended my 2 years with at&t and due for a upgrade shod I get the 7+ or hold off for the 8 at this point
Not even with VoIP apps and such
You can also use FaceTime to make video and voice calls to iOS devices and Macs.The iPad does not have the hardware to make and receive calls. You can use certain Apps like Google Voice to make calls over the internet.