It's worth reading up on machining processes, it will inform your questions.
You will need at least 4 axis for a herringbone gear, provided your machine is rigid your part will be as it is in CAD, you control the finish with the options in CAM.
"Polished" finishes are achievable with machining, the finish is a function of how fine the finishing pass is, the finer the cuts, the longer the time taken.