Nope. As long as you don't have an FTP server running. Also expect some "left the game" messages as script kiddies assume it's an FTP server and try to hack it.
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I disagree with you, therefore you are wrong.
Quality of output = Skill * Effort
Unlikely. It's usually recommended you forward ports over 10000 for maximum protection (usually vulnerable port scanners only check the most common ports, which are lower numbers). There are some other low number ports you could use. But 21 should be okay.
Quality of output = Skill * Effort
Impossible. It's like trying to bypass a combination lock with a lockpick.
Quality of output = Skill * Effort
Quality of output = Skill * Effort