#1 yes it is most common for the lower cabinets to have no top other than the countertops applied.
#2 My shop uses a prefinished plywood that has a Ultra Violet cured Polyurethane on it. We don't have to finish the inside but if you were to do that finish it before assembly.
#3 We hang the doors as we assemble the cabinets, before installation. The hinges we use have plenty of adjustment and allow us to do that. If your hinges don't have a lot of adjustment you might should wait until installation.
#4 Seen it don't like it either.
#5 We use only plywood for carcasses and solid wood for faceframes and doors. It don't make sense ($) to make the carcass out of solid wood.
#6 We have just recently started making our own crown.
#7 We buy from a wholesale house. Louis and Company
I once heard that cats and women will do darn well what they please and that men and dogs would do well to accept it and just go on.