I can't answer all of your questions, but I can answer some because I had direct experience last November. We went to MK on a party day and weren't staying for the party.
1) On the day we went (Sunday, November 12, 2017), there wasn't a morning EMH but the park did open at 8:00 am, which we took advantage of, and it was great...we hit several rides before our first FP at 9:30.
3) My understanding is that if you don't have a party ticket, you can't get in line for a ride after 6:00 pm, but if you're already in line at 6:00 pm, you will be able to ride that ride. When you get off the ride, the CMs will be ushering non-party people toward the front of the park. You will be able to shop and linger on Main Street until 7:00 pm. You can go eat at a restaurant before 6:00 pm - CMs won't rush you, but after you leave the restaurant, they'll be gently ushering you toward the front of the park. We had a 5:50 pm BOG reservation and didn't leave the restaurant until after 7:00 pm - CMs were lined up on the path to the front of the park checking for wristbands and if you didn't have one, you were limited only to that path.
4) I'll speak just to my experience on this one, but keep in mind that we were a party of 5 adults who had been in MK all day. The park, and especially Main Street, got incredibly crowded after 4:00 pm, to the point that my party of 5 found it difficult to make our way back down Main Street from the front of the Emporium to get to our BOG reservation. We spent the time between 4 and 5 shopping, but given how crowded it was, I don't think we would have chosen to wait in line for rides at that time anyway. On top of that, we were able to get nearly every ride and show done between 8:00 am and 4:00 pm. So for us, having a TS reservation just before 6 was perfect, and if we had the two reservations you have, we would have chosen to keep the Crystal Palace one.