If I am going to put chair rail up in my basement, is there a reason to mud/tape the joint first? I hung the dw horizontally...I can do it but I make a hell of a mess...dustwise...

Also, is there a particular height for the chair rail...The one wall will have a sofa and I do not want it rubbing the wall...I am usure if a sofa is at the usual height for chair rail though and I'll need to follow that height around two other walls....I do not want it to look too heigh or low....

Thanks!