Hello!
Good questions. I think most of your questions were answered by Merco_61, but I'll weigh in as well.
To go a bit in-depth through your lens question, there are a few things you must understand. The Nikkor 18-55mm is Nikon's stock lens that comes on most of its D3000-series DSLRs. It's called a "kit" lens because, well, it comes in a kit. You can take a pretty wide range of pictures with it, from macro to landscape, but it won't produce the visually stunning results that a lens designed for either will.
That's where the Zoom and Wide Angle adapters come in. Essentially what you're getting is a piece that will thread onto the end of your kit lens and give it a little more reach or a bit of a wider angle. Like Merco_61 said, they're pretty bad for sharpness.
As a rule of thumb, the less glass between your subject and your sensor, the sharper your images will be. If you're not worried about being able to take pro-grade pictures right out of the box, then sure, that's a great purchase! If extreme clarity is important, though, I'd steer away from that.
Filters are handy. As has been established, the UV filter is a throwback to film cameras. If you're shooting excessively bright UV sources like welding or the sun for long periods, you may want to throw that filter on there, but it's generally good if you use it similar to a screen-protector on your iPhone. It prevents your front element from getting scratched up and is a cheap alternative to a lens cap.
Polarizing filters are nice, however. Their primary use in photography is cutting through reflections and glare. When I shoot tidal pools or large bodies of water, I use a Circular Polarizer and the images come out much less white and with a lot more underwater detail.
Ultimately, it's up to you what you want. It sounds like what you're getting is a solid setup. One of my cameras is a D3000 and I love it, and a buddy of mine recently bought the D3200 and has been putting it to good use, so you're getting a good camera.
I can't really recommend lenses or accessories until I know what kind of photography you'll be doing--macro, portrait, still-life, landscape, action, etc--but the stock lens will do well for you as you learn.
Any further questions?
Noah