Though Sago is not a necessary ingredient, I suggest you add it since it gives a texture to the payasam.
I used around 260 gms of jaggery. You can adjust the qty to suit your requirements. Also, if the pumpkin is sweet, adjust the qty of jaggery accordingly.
Keep in mind that the payasam tends to thicken as it rests, so adjust the consistency accordingly.
It keeps well in the fridge for 3-4 days.
I use Maggie Coconut milk powder. For 1 cup thick coconut milk - I use 3-4 tbsp coconut milk powder and 1 cup water. For medium thick, 2-3 tbsp of coconut milk powder to 1 cup water. You can take this as a base and adjust it to suit your preferences.