Sorry, no. I'm not a designer.
I think a little Android in combination with the word "FTP" would make sense. Or an "classic" network symbol with an Android. Maybe some designers are reading this.
It's there for the easiest usage: if I disable it, a newbie user would be force to configure options and will probably look for something else...
OK.
I can't help you with this. I just can say that every other (working) FTP server I've tested is closing the connection properly.