Our daughter wanted a rock wall on the back side of our playhouse. So, we ordered a set of 20 holds, to see how far it would take us. It arrived with all screws, washers, T-nuts, and the Allen wrench. While I am a proud owner of a hammer, my available drills did not include a 7/16" - so I had to order one.
From there, it just took a few afternoon hours to the job done. It started with a sketch. Based on our estimates, for kids, a reasonable spacing of adjacent holds would be about 1ft vertically and 1.5 ft horizontally. This lead to the following sketch (the grey areas are some wooden pieces where we could not mount the holds).
We laid out the holds in front of the playhouse, according to the plan,
and marked the locations for the holds on the playhouse.
We drilled the holes for the first bottom piece,
hammered the T-nuts into the holes from the backside (= from the interior of the house),
and fixed the hold with the two screws.
Everything looked good, so we repeated the whole procedure for the other 19 pieces.
The result looks good. It turns out that the 20 holds are really sufficient to cover the whole backside. And we have a very happy climber.