Why does my Numbers doc with a few photos get BLOATED?

Is there a simple way to control the resolution (quality) of photos from within Numbers when I want to email them by XL? I want to be able to reduce the res to avoid large file size for emailing.

When using the mask function within Numbers is the final result similar to cropping in regards to the "size" of the photo? In other words, if I mask a large portion of the photo am I just hiding it from view or am I cutting it out so it doesn't add to file size?

I added some photos that I new to be 2-3 MB each to a file. When I tried to email the file in xl format Numbers balked and didn't even save my email. Frustrating.

I reduced the size of my photos drastically, but still the seem to puff up my document. I think the photos should have totalled less than 1MB but the file ended up being 4MB.

Thanks.