ad 1. PocketBook InkPad Color 3 would be nice for A4 documents. It's quite hard to reproduce (readable) such big page size even in landscape mode on rather small screen. But yes. it's possible. Especially if it's text in two colums. Not as fast as on modern tablets but it's acceptable while reading page by page;
ad 2. According to user's manual, you can use up to 128 GB microSD card;
ad 3. Screen resolution is 300 ppi for bw and 100 pi for colors;
ad 4. You have to use a case. Any other protection like foil will downgrade brightness and contrast which already are quite low. I suggest case with stand function and silicone back, like in this article:
http://cyfranek.booklikes.com/post/3...aliexpress-com
You can find some more info in this review:
http://cyfranek.booklikes.com/post/3...tnik-w-europie