Nipples seem to low after breast reduction, and scarring is stretching. Any suggestions?

It may be necessary for a revision in the future as your nipples are already low. I'd wait at least 8-12 months to let everything heal and settle. Usually upper fullness, that most women want, is only achieved through an implant and not through lifting alone. Scars usually take time to mature and fully healed and you might heal well enough or may need a little revision in the future.

You have several questions.  Pain:  this could be because not enough was removed, but you might also have inherent back issues such as disc disease that could be causing it.  If nipples are too low, this could be revised and improved.  You can't really get more fullness with a breast reduction without placing implants.  It is reasonably common to get widening of the scar around the nipple; that is dependent on how you body heals, but I would wait another 6 months or so before deciding if the scars are unacceptable because they take a long time to mature.