Tried a straight comb

1 - Straightening won't affect growth.  Like any heat styling, it isn't good for hair, but you can limit the damage and dryness by applying a heat protective product to the hair before styling and also by using moisturising shampoos and conditioners.

2 - You can wash your hair as usual although there are some shampoos and conditioners designed to help to "encourage" hair to be straight, (like Garnier Fructis Sleek and Shine).  However, it isn't necessary to use them, any products will do APART from anything that says it is "volumising", avoid these as they will make it very difficult to get a sleek effect with the straightening iron.

3 & 4 - Apply a serum to your hair when it's wet, one that's designed to reduce frizz.  This is necessary whether you want a wet or dry look when it's finished.  Depending on how long your hair is, you could use a small amount of gel to get a "wet" look although personally I've never tried that so I'm not sure how it would turn out.  To get the dry look just use the serum and the heat protective product when you straighten (like the L'Oréal Thermo one advertised by Beyoncé; there are lots of other kinds too, just look on the shelves).

Good luck!