RE: grainy bottom surface of the freesex wood
1. I don't know what the weight difference might be, 100g maybe. But I also don't think the "stonewash" finish is neccesarily any weaker. With thicker paint, you can always get into problems with the pain flaking if you hit in. Starboard still has this kind of finish on many race boards, and they sell many, many of these every year, so that is why I think your problem relates to your particular board and not the finish as such.
2. The wood is impregnated and "sealed" but since I don't know exactly what the problem is with your board I would again say the safest thing is to let the dealer have a look at it as soon as possible.