To fix preview image:
back up your map elsewhere.
Delete all files. make a new difficulty with one note and no background then full submit.
Repeat adding in the background you want. Clear cache in between reloads. If this doesn't work, or you have already tried it, oh well. Not much we can do about it. Perhaps changing the name too will work.
[skin]
default hitbursts

If you just want to use the default, why even bother including them? Hitbursts are one of the most annoying things, so most people have their own skin which uses custom ones.
fruit-plate.png is unnecessary
you have 2 fail-backgrounds
spinner background: Right now the vomit color is bleeding over the pictures. Could you make it slightly smaller than the pictures? also could you make it 1024x692 and with a black background? It looks bad because it snaps to black rather than fade to black.
SkinPreference:Default is one of the dumbest things you can do. If you really want to do it, then delete all the duplicated skin files in the folder, but I'll hate you forever. I can't customize the default skin. It would be nicer to find a decent vocaloid skin and use that, so we can at least customize it.
[storyboard]
When you use 640x480 images, only use "centre" and bring them in at 320,240. Otherwise you won't cover all the edges. It's an error in osu. Coincidentally, the same thing happens on the default spinner-background, which is why you should use 1024x692 rather than the default 1023.
34286 - start fading out here.
[easy]
01:34:286 (1,2) - This feels weird to map in easy. There's no clear beat (it's a drumroll) and this is just after a break and silence, so I lost track of the actual beat.
[normal]
You've done a great deal to make the map look as good as possible, so I thought I'd point this out:
01:03:429 (1,2,3) - These don't stack perfectly:
http://osu.ppy.sh/ss/105753[ignore this mod]
02:42:858 (1) - Normally your sliders are the perfect lazy-man sliders (not perfect but don't look bad), but this one really stood out as ugly.
[insane]
00:57:000 (2) - I don't think the jump fits, but at least space them evenly
01:06:000 (7,8,9) - Anti jumps

01:34:072 (1,2,3) - don't map this
01:42:000 (5,6) - fyi these are groups of 4 in the music, I don't think there would be a problem with putting a note on the last blue tick on an insane with a jump in the middle.
01:49:714 (5) - This doesn't really fit the rest of the song's sliders, but okay.
02:23:143 (2,3,4,5) - These feel more like jumps to me. Accelerated spacing is for increases in intensity
02:31:072 (1,2,3,1,2,3,1,2,3,1,2) - this would be better to put accelerated spacing
03:26:572 (9) - don't cover up repeating sliders (another reason I hate these hitbursts), and this is just a weird place to put a 2x repeat.
03:21:857 (4,5,6) - see [normal]
03:33:429 (10,11) - switch these to better match vocals?
03:46:929 (4,1) - bad spacing
Very nice, only a few real errors.