Any player that is Ready on the playing field can tackle the ball-holder, regardless of their relative placement on the board.
Yes you can, as long as there isn't a Sin Binned player in the team. The slot is there to provide a disadvantage only when a player is sent off.
The #10 can be specifically searched for and put into play as a SUPPORT Action.
We figured it was easier to have it double-sided so you don't need to look through the Back deck to find it, then have to shuffle them.
Not at all, the game plays perfectly fine without them. In fact, we suggest you leave those cards out until you are comfortable with the general gameplay.
In short, because it's Rugby (you should see the actual rulebook for the game, it's huge!).
We feel we made a good balance between keeping the feel of the game with enough of the main actions covered, and not becomming tedious.