Does charlie work as a first name? Not as a nickname for [name_m]Charles[/name_m], but just [name_u]Charlie[/name_u]?
Yes, definitely, and for boys + girls.
I adore [name_u]Charlie[/name_u]. [name_m]Charles[/name_m] is okay, it’s a family name, but I much prefer [name_u]Charlie[/name_u] as a stand alone. I have [name_u]Charlie[/name_u] [name_m]Hawthorne[/name_m] on my short list.
Obviously 
Yes it works! I used to babysit a little boy named [name_u]Charlie[/name_u].
[name_u]Charlie[/name_u] is great as a given name. It has long since passed into the realm of acceptable full names.
Definitely. It’s in use enough by itself not to seem too nickname-y. To me, [name_u]Charlie[/name_u] has a much different vibe to [name_m]Charles[/name_m], anyway.
Definitely. It’s number 4 here in the UK. I personally prefer it to [name_m]Charles[/name_m], if only it was less popular. 