Whitespace in filenames

I have inherited some code that looks like this:
if [ ! -f $file ]
then
echo "Error Can't clean >$file<. May have spaces in the
name?"
else
mv "$file" DEL.$file
fi

I have these questions:

a) can it be rewritten as if [ ! -f "$file" ]...
b) change the mv as mv "$file" "DEL.$file"

Thanks for your help

.