I think you definitely need voice therapy, sometimes it is nice to have some done before the surgery, in order to know if it works without surgery, maybe. Some techniques learned in therapy are applicable post op, others are not (and may even be distracting). But be advised that in most cases a voice therapy is needed because te surgery changes pitch and some parts of timbre, but it cannot change all that makes a voice sound male or female - the surgery can maybe do 30% or so...
Complications are possible - permanent hoarseness , not enough increase in pitch, lower volume, decreased pitch range are complications that occur temprary or can occur permanently to some degree, depending on the surgeon, skill, technique and luck.
Severe complications can be a suture that rips or dissolves prematurely - in the latter case it can be corrected with another surgery (one is safe from that one with Dr Kim who uses permanent threads) - in the first case, which usually only would occur if one severly disregards post OP restrictions (no speaking for 2-4 and absolutely no shouting for 8 weeks). If it should occure, the complications can be severe though, but really , this is all about planning to be in a calm environment post op.