Chin Liposuction to Fix Witch's Chin?

You have many questions which are difficult to answer without an examination.
For a true withches chin the best way is probably a scar under the chin to remove excess skin and fat.
It would necessarily leave a scar that would be concealed in the chin crease.
It would probably be 2 inches long.
Costs can vary from 2500-6500 USD under local anesthesia.
Sutures are generally removed within a week. Activities are restricted for 3-6 weeks.
Surgery carries risk and you should discuss this with your surgeon

Witches Chin is a condition in which the tip of the chin "hangs down" and is more properly called Chin Ptosis. When viewed from the side, the chin typically hangs down below the line drawn along your jaw line.

Correction of the "Witches Chin" requires a fairly minor surgical procedure done through a small surgical incision through the chin crease or sub mental crease beneath the chin.

Witches Chin is usually seen in much older people in their 60"s and 70"s not in a person in their 20's. Your doctor should be able to examine you and determine if in fact you do have Chin Ptosis.

If you actually have a "Double Chin", excess fat and skin of the neck below the chin then Laser Liposuction would be the proper method to correct a "Double Chin":

Doing Liposuction in a person who truly has a "Witches Chin" could actually make the Chin Ptosis worse by accentuating the chin by reducing the fullness of the neck on profile view.

The best way to fix it is by making an incision in a naturally occuring crease under the chin, then removing extra fat and muscle tissue from the chin. Liposuction alone will not achieve that.
Regards