OK, now we've had a bit of fun, seriously, welcome to the forum @jas1vans
I appreciate the enthusiasm and many of the answers you seek you will find here. But to stand a better chance of getting responses from the community, try to keep it to one or two questions per post. Someone would have to post a short novel here to answer all your questions!
Ebay is a grear place to determine prices. Look at the sold section to see what things go for. Grading comes with experience. There are guides and books, but you learn from experience and it's not an exact science. Just check out the current grading contest here to see how 'experienced' opinions vary!
If you put in the work, you'll soon be able to tell high grade from low, very fine from very good etc.
Well done giving away the boxes to the kids. Great move.
Good luck