Is a gum lift/ gingivectomy before veneers necessary for me? How many teeth should I get done if so?

Wow what a great veneer case this will be.  Without question, you will want to do some gum recontouring on the front four teeth before placing veneers. You lip looks lip it raises really high when you smile as well.  If you still show excess gum tissue after the veneers are completed you could have a procedure called lip tacking.  This is a surgery that will keep you lip from pulling so high when you smile.  Best of luck.  

To gain the best symmetry you will benefit from gum lift (gingivectomy / esthetic  crown lengthening)  all the way to your back teeth. Even though you are not going to veneer them ...This is because in your profile pics You have a gummy smile which extends to the molars .....

Absolutely. It is ultimately important that beautiful front teeth, match and are mirror images of one another. They are the "stars" of your smile. As in any cosmetic smile work, we start from the front two teeth. With placement, size, and length. Then examine the surrounding teeth to make sure all match in harmony. That is how a decision is made whether only 2 teeth will do the job, or placing veneers or crowns on surrounding teeth will much improve the smile