1. Wipe data/dalvik/cache via recovery.
2. Flash the Slimkat ROM and GAPPS via recovery.
** You already have the 4.3 (.205) kernel installed. So, no need to flash the kernel via flashtool.
** The ROM has built in recoveries.. Press vol buttons when red LEDs leading to a vibration.
** Keep a full cwm backup of your current setup, just in case. (BTW, Restoring .205 ROM's data into Slimkat didn't work for me)