If you want unfinished, you should be shopping at a local retailer that buys it from a local mill, not internet crapola. Prefinished is far tougher against wear and tear and easier on you to put down though. You don't have to move out everything and yourself to do the project and then wait for it to cure. You can shift furniture from room to room and do a room at at a time with no issues.

I can't comment on your questions 1, 2, or 4, but I recently built a custom house and installed Build Direct engineered, prefinished, 5-inch plank handscraped Durham maple hardwoods throughout (roughly 1700 square feet of flooring). Like you, I read many bad reviews for both Build Direct and their product...but I took a gamble and ordered anyway. I had no problems with Build Direct, with delivery, with the product or anything else. Maybe my experience is the exception, but I love my hardwood floors and people comment on their attractiveness all the time. During the install, I asked my contractors if they noticed any quality problems and they said they did not. I asked if they noticed a great number of planks that could not be used and they said they did not.

Also, from what I have read, prefinished and engineered hardwoods are more stable, meaning they are not as prone to expansion/contraction as unfinished. That's why I chose the product that I did.

I haven't taken pictures of my finished house in quite a while but the picture I am attaching shows the flooring. This was before the house had the final cleaning, so they are very dusty. Still, I think it gives you a general idea. My house has been finished for 5 months and I honestly could not be happier with my floors.