Welcome aboard. It's a great contest. Hop into the 9 Blazing Months if you want to get started.
1. It usually gets announced at the end of November/start of December. That's when I'd be expecting it.
2. At the same time as the contest is announced. That said, you can post in the General Discussion forum now (as you obviously did with this thread) and some of those threads get advanced to the new forum. At the time, you'll see the contest logo up with the other logos on the top left and that'll link directly to the forum.
3. That's changed every year (initially, I don't think they even said what the challenges were, much less the "twists"). Typically, the twist has been announced when the round itself starts, giving the contestants three days to work. This past year, they let everyone know a bit earlier -- a lot earlier when it came to the Round 2 entry. Personally, I really liked knowing the twist earlier as a fan; as a contestant, it must have been a huge help.
4. Assuming the rules are the same as previous years (and there usually is some tweaking), cursed items are not allowed. As for drawbacks, you'd have to be careful, but you could look at 2012's sticky pugfoot for some idea.
That said, last year was the first year they had public voting in the first round, and it certainly seemed like Paizo was happy how that worked out so I'd absolutely expect it again. It's possible they could decide that not having the judges have to weed through every entry means they can expand it beyond Wondrous Items, but that would surprise me (every year there's some complaints about that challenge being limited, but it's been explained that it's a design space that leaves a lot of room to play with while not being so huge it can't be judged).
Anyway, considering the nature of the voting, I'd personally be very careful about doing something with drawbacks. While some voters may be looking just for that spark of mojo, others will likely be looking for things they go "cool, my character can use that!"
I'd highly recommend looking through previous years to see what's been done, specifically the Top 32 each year, but also the Critique My Item threads. You can see a lot of pitfalls people regularly run into.
To paraphrase the judges responses on cursed items. Ask yourself this...
"What is wondrous about a cursed item?"
If you can't find anything the players would find wonderful, then it's not a wondrous item.
This round 1 guide is a good place to start. It also links back to the originating threads and so will save you a lot of forum wandering to find things out.
And this thread is this years' annual practice thread, come join us!