Login Page / Admin Slug

I have three questions regarding changing the login page URL / admin slug (not, though, changing the login page as it relates to cookie brute-force prevention).

1. Can I use symbols, in addition to letters and numbers, in the login slug?

2. Is there a limit as to the slug length, in terms of letters / numbers / symbols?

3. Can I change the login slug as often as I’d like?

https://wordpress.org/plugins/all-in-one-wp-security-and-firewall/