Clay pot is used for fermentation , as science says it provides micro-oxygenation, including enzymatic reactions for producing unique flavors. If you don't have clay pot , you can use steel or glass vessel but clay pot is recommended.
Fermented rice needs to be mashed well , you can either squeeze with clean hands or use fork or blend in a mixer.
Use slightly sour curds , it adds more taste to rice kanji.
Tempering with coconut oil adds lots of flavor and tastes really good.
You can use any type of cooked rice , best way to use left out rice.