I have a list that is very similar to yours, probably because we both searched "manifest" and "morph" in scryfall and put in the best cards, haha.. But let me tall you - it is so much fun. The combat tricks and mind games you can play with morphs! And you literally have a better Rhystic Study-on-a-stick as long as you have Kadena + Flash. I have actually ended up having too much card draw, and over-extending too hard because of it..

Some cards that could be really good in this list:

Alchemist's Refuge and/ or Emergence Zone - Flash is the most important and best tool you can have in this deck, and these are both decent option on a land.

Craterhoof Behemoth - has haste, and can really amp up your threat level. Is in many ways just a better Biomass Mutation

Ugin, the Ineffable - Your morphs cost .. Combined with Dream Chisel , your morphs are free WITHOUT Kadena out.. Nutty

Beast Whisperer - Basically a replacement Kadena minus the discount effect.

Evacuation or other symmetrical creature board wipes - This deck is one of the rare decks where bouncing your creatures can be really good. Gives you repeatable card draw, ramp and tools and tricks. Evacuation is definitely the best, mostly bc of instant speed, but I've found Flood of Tears to be decent. (90% of the time you want to replay Leyline of Anticipation ...

Fun to see others appreciating Kadena, Slinking Sorcerer ! I actually think she can be deceptively strong, and has real potential!