RE: 7 inch tablet for reading
I would personally not recommend to use a 7 inch Android tablet for reading as it will not be able to show much text at a time, you may even choose a 7 inch tablet for reading if it has got a good screen display resolution, higher pixel density is very good for crispness of text and it allows much easier reading without much strain on our eyes.
I would highly recommend to use a 10 inch tablet for reading purpose. A large screen is very effective special in reading purposes. You may even go for a 7 inch tablet if you are low on budget as a 3 inch screen does not matter too much.