the tablet used should have no impact on image quality, you may prefer the performance of one for the FPV experience however.
Controller battery does not need to be discharged to storage level if that's what you are asking. Your question isn't clear, to me anyway.
My neighbor bought one. I set it up for him while he was at worked. During a break in our miserable weather we gave it a test. Must say I am looking forward to mine. Hoping my Mavic ships soon. I'll have plenty of toys to pass my time.It's not just the weight difference, I think you'll find the P4P+ remote is a real convenience.