Re: image slicing
The slice tool is used for Web Pages so don't use that.
The "easiest" way, I think, to accomplish your goal would be to merge the layers and then use the lasso tool to make your selections. Once a selection is made a simple Copy / Paste will give you the "slice" you are looking for.
Make sure you save a backup of your image before you begin in case something goes horrible wrong - you cannot unmerge the layers once merged.