Important a good screen, so no glare, and with sufficient resolution.
Brightness is measured in candelas per square meter (cd /m2) the more the better. Ideal - AMOLED or retina
On account of the size don't know, I would like to hear the opinion of used 7" and 10"
Only ten, seven is nothing like a big phone. You can use 9" being a iPad, and have kitaeveda with this retina.
In addition to screen, other specs are not important
You need minimum HD, and at 10' you need a large resolution and pixel density of PPI as they will be seen.
from the battery more than a few hours is not necessary,
8000 mAh at least given the fact that akum is rapidly degraded
Advise tablet.
Here's the problem, as they mainly China and of poor quality.
market.yandex.ru to help