I am soooooo confused!!!!! I don't know if I should switch or not! Is there much difference between deck 8 or 7? I"d be moving from deck 8 port to deck 7 starboard
Everybody has their own preference, and I don't think there's a definitive "best" choice. But I understand your concern; I agonize over booking decisions, too.
We sailed port last time, and it was fine. It was cool to see several ships passing in the night--not sure if that is more prevalent in the port side (sounds like it is from posts above). However, we preferred the starboard view of Castaway (from the sun decks) to the view from our room. I can see how others would like the port side, though, and do remember the CM's waving goodbye with the Mickey hands, which was pretty cool.
I also agree that 99% of your Castaway time will not be spent in your room, so I wouldn't worry about it too much (again, even though I am guilty of splitting such hairs as well).
Fireworks would only be an issue if you didn't make it up to 11/12 for Pirate Night, which I would recommend over your room anyway.
Since we did port the first time, our next cruise in February will be starboard to try it out. But if we did starboard last time we'd probably be doing port this time. I don't think it will impact your cruise at all. I prefer a higher deck, and while 7/8 is basically the same, I'd say stick with 8. But most importantly, don't worry about it!