I have an 8-year-old engineered hardwood floor (Hartoco Beaumont Plank) with slight moisture damage to the surface. The surface has cracked and/or flaked off at entrances to the home. I am good with refinishing furniture by hand and wonder if I will be able to refinish an area about 2-3 foot without it being noticeable? The floor has a 2mm wear layer.

Will I need to re-stain or just sand and apply a natural finish?

I have a few dozen planks of the same batch. Am I going to likely be happier with just having it replaced by a professional than trying to refinish it myself?

I think you will be happier in the long run having those boards replaced. One draw back is they may not match exactly in color for about a year or so.