When I built a a8 llano pc for my gfs mom, I used the stock fan and it was quiet. Granted that might of been because of the fans on the case were louder.
Yeah the case i chose is not the best but its closed with a little bit of side soundproofing. it looks nice and minimal. its not for me though.
Im a little concerned about the quality of the stock fan so i think the best thing to do would be to build the system with stock parts and see what happens. thats part of the the fun right!? take out whats bad and replace with good parts.
what i'll do is make the build and post the findings. maybe ask for help if i get stuck for choice.