Just start working on it, dont worry about saving time, anything you learn in ActionScript will help you eventually, if not on this application, on another one.
Also, when asking for advice, be more specific.
If I were you, I would make the crossword puzzle by hand, draw it out so its all ready to go. Then build a movieClip that looks like the crossword puzzle. have each box be a separate input text box. Use if/else’s to check to see if the letter is correct. If it’s correct, fine, if not, change the color to red or something. Or have a “check words” button that runs thru the function to check to see if the letters are correct or not. if they are, fine, if not, they turn red or get erased, whatever you want.