1. You have to Unlock bootloader, Root, Flash kernel which is suggested in the 1st post, then rom. It is always better to reset everything when getting to new rom, especially totally different version of android.
2. First time, factory reset, next update of Ka will not delete Data partition so ur data will be saved, if you have trouble, then you can try Resetting all and reinstalling.
Hope this helped!
Thanx for the explanation. I'll try when KA19 has arrived.