Two additional checks not mentioned.
When you feel the nut is tight enough, grasp the outside edges of the tire and rock to check for play in the bearing assembly. If it rocks either the bearing is not tight or the spindle,race has excess wear.
After final assembly take the trailer out on the road for 10-15 miles, stop and go feel the temperature of each bearing hub. One that is warmer than the others is probably too tight. Your next trip check the bearing temps again after about a hundred miles.
I replaced many a bearing set on boat trailers used in salt water and spindals/races will corrode and loose the hard surface.
pops