Hello and welcome to Amiga.org!!
Kickstart 3.1 IS the same thing as the 3.1 ROM. So yes you need both the KS3.1 ROM and WB disks.
As for partitioning and repartitioning? You could just install the 3.1 as an update and leave everything in place or you could start from scratch. Partitioning and such on the Amiga is very easy. Just use the tool HDTOOLBOX that is on the INSTALL disk that comes with OS3.1. As a matter of fact BOOT the Amiga with the INSTALL floppy and then use the HDTOOLBOX on it.
Sorry but I am not familiarwith the FastCard Plus.
