@Mannyrock This may give you some ideas. I see some similarities between the ways you've described your grandson and the way my daughter at that age liked to "read" for long periods of time (for her age), liked playing with things she could move herself, was careful and did not like loud noises.
I decided to buy her first train set (she calls it the Santa Train) when she was three. I spent about 3 weeks putting together the basics of the layout seen here which was low enough that she could reach everything she might find interesting from the plastic stool she could move around herself (pictured below). I tried to include lots of interactive elements that she could control herself, with the occasional help from Dad if she needed it. She liked to move the O gauge figures (especially Santa) around the layout, operate the milk loading platform (onto a flat car so she could see it happen), dump logs using the operating track, same with the coal dump car, add coal to everything (even it it wasn't a prototypical use) and especially "drive" the automobiles around the road on the perimeter of the layout. Later she enjoyed running the trains, painting the bench fascia and adding more scenery and figures. Even though she's older now (at an age where most kids would rather be on their iPads), she still enjoys running the trains with Daddy when we set them up each Christmas in a temporary floor layout. She's really looking forward to our next "real" layout. Hopefully coming soon.
She also doesn't care for loud noises. When she was 5 we went to the "Train Museum" in Roanoke,VA and she really enjoyed that too, no loud trains there, just parked ones.
