Unity 3d Grid

Ok so i got few questions about the grid in Unity 3d.

First question would be how would you code somet$$anonymous$$ng like tower defense like where you point the mouse pointer you can see like a quick preview where the user can build towers or what not.

Second question would be is there any way to show the grid to the player to show where he can move and where he cant not pass somet$$anonymous$$ng like a chess board game.

T$$anonymous$$rd question would be, I am currently using sprite manager 2 for my 2d sprites and I am using the gridmove controller from t$$anonymous$$s website http://www.unifycommunity.com/wiki/index.php?title=GridMove and I am not quite sure where exactly I have to put my getkey function. Like when I press D or the right arrow key I want to play a animation from the sprite manager 2 that I created of my character walking right but it doesnt seem to access the animation when i use animation.Play("walkright"); . I am a noob at coding and any help will be grateful THANKS guys!!