for the file sizes, i think that is becasue you are exporting in full 1080x1440 or whatever you said vs a slightly smaller 1280x720p hd size. (this is what i mostly use for online videos). its still hd at the smaller size and will reduce your file sizes but you might not get as high a quality on something like vimeo full screen is all. if you wanted to keep the resolution the same and you have compressor, i know you can limit the size but there may be some quality loss if its saving way lower than what you exported.
as for final cut saving all of your footage clips do you mean they are duplicating or are they just the raw clips? in order to edit in final cut it needs those clips. they aren't stored permanently in the bin that you see when editing, its more of a "file path connector" if that makes any sense. the bin is getting all its clip info from that original clip saved somewhere on your hard drive, if you were to delete those, the next time you opened your project you would get errors up the wazzu saying that the media went offline. so unless you are completely done with this edit and never want to use those clips again, i would keep them. if they are duplicated for some reason or you don't want them, then you can trash them
i recommend getting an external hard drive tho if you don't already have one because videos will eat up any available space faster than a fat kid in a candy store