Disneysea is it very different/special? I first time go Disney land
Are there special events like fireworks every night?
Is it safe to go back hotel alone late from disneysea?
Is there a queue for single riders (like in USS)?
Gumxia
Not sure if they have special events every night, but I went on a weekday (Thursday) and they had the shows and fireworks etc. Subjected to weather conditions though I caught the performance when it was drizzling heavily like you-definitely-need-an-umbrella-kind-of-drizzle. And the performers were wearing transparent ponchos. So if it's not pouring, pretty good chance you'd be able to catch it still.
Left about 8 plus and by then most people were alrdy leaving. But as someone mentioned earlier, Japan is pretty safe!
There are single queues for most rides but not for the Toy Story one for sure. That is the most popular ride and fast pass ended at 11am when I was there. So if you want to have a go, be sure to be there latest by 10am. This is one fast pass you have to take first once you get in!!!! Otherwise, be prepared to queue for 1hr or more. For single riders, you'll be joining the fast pass queue and it will save you more than half the time since most fast pass Q-ers are in groups. You'll be allocated a seat when they need the space to be filled. Was in and out of the rides in less than 20mins for single rider queues (even for popular ones!) then again, depends on which day you go!
Everything above is for Disneysea not Disneyland since I did not visit Disneyland. Hope it helps!