The iPad is not a phone, so selling your iPhone and keeping the mini would leave you without a phone at all.
If you don't need a phone, it should be fine as it does have a bit better camera, but the size alone would deter me from using any iPad as a camera. The iPhone 5 takes very good photos and I doubt many amateurs would recognize the difference between it and the iPad mini 4 in quality.
There will be a flashbulb of photographers around shortly to express their shock and contempt at the notion of a mere iOS device comparing to a "real" camera, or someone's main camera (even though in fact, the iPhone is the world's most popular camera by some considerable margin).
I enjoy the cameras in Apple products, but they are really ideally used for two particular types of photos: outdoor with good lighting, and those that do not require zooming. A camera you have is better than one you don't of course, but an iOS camera is not ideal for all kinds of photography, and compares really poorly to DSLRs (for example) in a number of areas.