Your plan sounds great and there is no reason to trim them unless you want to. In competition we trim spares in what's called the St Louis cut but that is for appearance only.
As far as when they are done there will usually be some pull back of the meat from the bone ends.
I use the bend or crack test to determine when they are ready. Pick up one end of the rack with tongs and the meat will bend or crack in the middle of the rack.
Another popular way is to pierce the meat between the bones with a toothpick. It should go in with very little resistance like butter.