sorry, ich meinte natürlich "formerly known as"

Ist mir vor allem seit Prince' "The Artist Formerly known as Prince" Spirenzchen ein Begriff.

Mir scheint die Abkürzung "f.k.a." - im Gegensatz zu "a.k.a." - nicht sehr gebräuchlich zu sein.

ist eher unüblich, findet man aber im Zweifel durch simples googlen. aka ist auf jeden Fall beseer

aka ist auf jeden Fall beseer

"besser"?

I wouldn't say that one is better than the other -- the mean two different things. "Formerly known as" would indicate a name change. "Also known as" would indicate that the person goes by (at least) two different names.

#3 is right. FKA/fka/f.k.a. is not used very often, and I would recommend that non-natives write it out (as was done in #2). Just because it can be found online somewhere doesn't mean it's terribly common or would be understood by everyone.