Unity doesn't contain the FBX files themselves, it's all converted to it's own mesh format and stored that way. Which should be a bit smaller than the FBX file.
'skin or die' might be the script you're after. www.scriptspot.com should have it. It contains a heat map or colorized display of what part of the mesh is affected by each bone.
UE4 doesn't support parametric modifier animations. So yes, doing it in the UE mat ed is the way to go. Also, your thread title contains an oxymoron. ;)
BTW before posting the character showreel I did posted the following post containing only still images.... http://polycount.com/discussion/178493/old-mercenary
i am quoting this post because it contains a very very high level of truthiness. tf2 was a fantastic game in 2008, and it's really unfortunate that it turned into what it is now.
the white is probably due to the video's encoding. what encoding are you using on the file that you are uploading? youtube works best with h264 encoding delivered in the .mp4 container.
It looks a bit boring atm. I would add some stains and scratches on the glass. Maybe also a corck on the top and a label/sticker with what the potion contains.