Unusual "Size" value displayed in Finder; meaning of arrows in Size column
The up arrow means the file is uploading. The reason for the unusual size is because that's the size that has been uploaded. Not the size of the total file. Once the file finishes uploading to your computer it will have a "normal" looking size and the arrow will disappear.
Downloading 4 files/folders at once will slow them all down. So just be patient.