Number of 2-d photos to create 360 photo and how to stitch them

Question

I am a VR beginner. I want to play around with creating a 360 photo from my phone's 2-d camera alone. From what I read it is a common case but I dont see any guideline one

1. Should I take regular flat 2-d photos or panorama?
2. What is the optimal number of flat photos/panorama to take for the VR experience (360 photo)?
3. Will OpenCV's stitching program work for both the kinds of images to create the 360 photo? I want to do this on my android phone so hoping to get pointers about doing the above in Java