You gave an excellent description of an acute gallbladder attack.
The size of the polyps may not be what is causing your discomfort. Some type of blockage of the bile duct could be doing that. Murphys test....when there is pain when the right upper quadrant (where you're hurting) when felt/pushed by your MD. So I guess you did not have severe pain or shortness of breath when it was palpated?
The HidaScan will be able to tell at what percentage your gallbladder is still working/or not working.
If you only had the small polyps surgery wouldn't necessarily be a consideration from what I understand, but it sounds like there is more going on...blockage of the duct by polyp, sludge(crystallized stones), or outright stones. Were you told if there was a thickening of the gallbladder wall?
Your #3...I have no clue, but do a search on 'gallbladder polyps with Negative Murphy's sign' and you'll get lots of information that might answer your question(s) better than we could here.
Gallbladder cancer is very, very rare, so that should put you at ease.
Good luck and let us know how you're doing