I know the question may sound silly but will you add a tutorial in the game ??

Yes. The first few missions of the singleplayer campaign will serve as a tutorial for the game.

Will there be several difficulty settings ? I reckon for the sand-mode it should be compulsory but for the campaign ?
Also how does the IA change when the difficulty evolves ? Does it get more ressources, faster ship-spaws or just better IQ ?