The simple answer is that grab adhesive provides sufficient strength, assuming a normal quality wall,
this is what I was using. On a blank wall, pencil in the top line all the way, I use a masonry nail that goes about 25mm into the wall as a locator to ensure full alignment and adhesion, the nails will also help straighten any irregularities in the wood, I drill before nailing to avoid splitting and counter-punch and fill to hide the heads, I use about 1 per meter. Without restriction, I would start in the middle and work out, where you have a mitre to join to, start there with an assistant holding the long end if needed and work away. If you need to join lengths for a run, use a 45 bevel, do not try to butt a square joint, it will be ugly.
I use screws and plugs to pull in picture rail or dado only where you want to follow an uneven wall without gaps, it shouldn't be needed for strength, but obviously if you are concerned about the state of the surface, then plugs and screws can be used, countersink and fill over to hide the head.