For me [name_f]Cassie[/name_f] feels a little dated, it was most popular in the US in the 80’s and i know a lot of Cassie/Kasey/Carries from that age group. However thats a regional thing and may not be relevant where you are. (And really there’s nothing wrong with a dated name!)
[name_f][/name_f][name_f]Cassandra[/name_f] would be my favorite long form. Others id consider would be Kassiani/Cassiane & [name_f]Keziah[/name_f],