Which cinnamon (dalchini) type should I grow and is true cinnamon different from cassia?

There is a real difference. True cinnamon (Cinnamomum verum, also called Ceylon cinnamon) has thin, soft, multi layered quills and a delicate flavour, while cassia is a thicker, harder, stronger flavoured bark from related species and is what much of the world bulk market uses. India grows cinnamon in humid tropical areas like Kerala, coastal Karnataka, Tamil Nadu and the Northeast. For the premium thin quill market you want true cinnamon types, raised from selected planting material. It grows as a coppiced shrub or small tree, you cut back the shoots and peel the bark from young stems. Confirm the recommended planting material and whether your buyer wants true cinnamon quills or cassia type bark before you choose, since the market and price differ.