Thanks for playing!
1) Yes, the max number on a block is 10 (once your merge two 9s, they turn into a 10 and disappear shortly after).
2) The time between new blocks decreases over time, but the max speed is one block every 1.4 seconds. Coupled with the fact that you can merge blocks until they disappear, theoretically you can get infinite points. :)
3) Yes, you can only pick up blocks that are in the indicator next to your character.
The gray blocks are just regular blocks and now have the number 1 on them, the screenshots are outdated.