1. This is not in the correct sections!
From your point, 420 usernames are kinda hard to crack because these are Minecraft usernames instead of email's! You'd need to crack a old account where Mojang did not release the update where you need to login with your email. Also you should use Kryptonite client for scraping alts! And Mojang usually blocks the proxies, so you'd need a good one! I have only cracked 1 unmigrated account so far this week!