Can stiches help in healing prosses in diabetes patient? Like C-section wound with stiches will heal better? As compare to normal wound?

No. Any foreign object in the skin can create inflammation or increase the chance of infection. Stitches are used if they have to be, to bring the wound edges closer in order to heal together.
It depends. It depends on the type of wound. Certainly surgical incisions and deep lacerations will heal better if they are stitched together or sutured. Regardless of the type of wound, good wound care and control of blood sugar are also very important. If you are trying to conceive, I would also recommend vigilant control of blood sugars and weight loss, as well as prenatal vitamins starting today.