We do not believe Jesus was the messiah. We do not believe Jesus was just a misunderstood good guy, whose reform efforts went awry. WeHaQelalah KeKhol-HaKatuv BeSefer HaTorah. Firkovitch did this in an attempt to alleviate the Karaite community from the taxation and conscription laid upon the Rabbanite community in Tsarist Russia. No one, however, in the academic community today takes Firkovitch's claims seriously.
Conversion is a misleading term.
Hitgayerut entails swearing allegiance to YHWH, His Torah, and the Jewish people. For males, it also entails circumcision.