It has been a week since you posted and no one has answered so I will give it a shot.
For fertilizer, any balanced one will do ie: 30-30-30.

Sun is fine for these guys.. they love it, you will just have to water more.
I know nothing about the rajapuri.. sorry.
Your DC can be seperated when the pup gets about 1/2 the size of the parent plant. Hope that helps.

Sorry for the late answer.
Bananas can be grown in full sun if there's plenty of water and the plants are fairly large. Pups like some shade. You can plant them in full sun and use a shadow-curtain, used for glasshouses, if it's too hot.
I grow the smaller plants in 30% shadow.
If you don't grow them for foliage, like I do as well, I should use a fertiliser with more K. Ex: 10-5-25.

What do you mean by: "it's grandmother stem" ?

Simon

I dunno, I read that term some one. I guess it would be more aptly named mother stem/plant, which I think it is.

How hot is too hot?

Too hot: the leaves fold together and bend over. Then the plant cannot take up enough water to keep the leaves up.
If you move them to more shadow (or give them more shadow), the leaves will come back in their normal position.
Simon