Is it possible to do V-Line Surgery before underbite correction surgery?

V line surgery would change your mandibular angles and this would not improve your appearance. I would recommend a vertical reduction genioplasty which will decrease the overall length of your face. The amount of chin projection needs to stay the same so that you maintain the mentolabial fold.

The photographs demonstrate a dorsal hump on your nose and a recessive chin profile. Consider placement of a chin implant to augment the chin forward for better facial balance and proportions. A closed rhinoplasty approach can accomplish shaving down the dorsal hump, narrowing the bridge line...

You have made a good self assessment. I think that V line surgery to diminish the width of the angle of your mandible, a reduction rhinoplasty and buccal fat pad reduction will help provide a thinner appearance to your face.