I love your questions! I hope I can help with some of them.
At MGM, the Stars & Cars Parade is in the afternoon and even 15 minutes before on a crowded day, you can still just sit on the ground to see it. I recommend looking at your park map when you're there and checking out the parade route.
At AK, we consulted the map for the route because we knew we wanted to leave right after the parade. I really recommend that you pick a spot to watch it near the beginning and before it reaches the park's entrance/exit. We walked behind the last float/truck after it passed us. This has Mickey on it. It was a blast to walk and see everyone else watching the parade light up when they saw Mickey. It's hard to describe seeing literally hundreds of people's faces light up when they point and say, "There's Mickey!"
At MK, we enjoyed watching the Snowglobe Parade in the afternoon from the steps of the WDW Railroad at the entrance.
At MK, the Spectromagic Parade is just get a spot if you can! The CM's are pretty good about keeping the sidewalks open. You have to have someone camp out a spot an hour early when it's crowded.