When can I get plastic surgery & stretch mark removal after delivery of triplets?

Tummy tuck. You may benefit from a tummy tuck to cut out extra loose skin and tighten the core abdominal muscles. See a board certified plastic surgeon for consultation.
Stretch mark removal. Stretch marks may be treated with lasers. This should result in some improvement; however, in most cases it will not remove the stretch mark completely. When you are done having children and have completed breast feeding, you may consider having a tummy tuck (abdominoplasty) which will remove skin containing stretch marks between the belly button and the pubic hair line.
Stable wt & no nurse. When you have achieved a stable return to your baseline weight and are no longer nursing, body contouring procedures may be considered. The soonest this tends to be approximately 4 months but preferably one year after delivery. Do not forget that you may need alot of assistance caring for your triplets after surgery. Good luck and congrats!
I suggest waiting 3. To 4 mos after delivery or after breast feeding done, whichever later. It takes several mos for your uterus to shrink back to prepreg size.
Yes. Laser re-surfacing is a common option but success rates differ depending of the severity of the stretch marks as well as the amount of tissue being treated (thin vs. Obese patients for example). There are other options available depending on the severity.