Q.Rooftop Gardening and Hydroponic Gardening
I have recently (a week ago) planted Fenugreek, Coriander, Tomato seeds in a grow bag with cocopeat and manure, which are placed in the terrace. I can see small leaves in each pot. The question is, how much water and sun is needed at this time?

6 to 8 hours of sunlight for herbs and tomatoes would do well with 8 hours of sunlight.
Here are a couple of articles.
https://www.gardeningknowhow.com/edible/vegetables/tomato/how-much-sun-do-tomato-plants-need.htm
https://www.gardeningknowhow.com/edible/vegetables/tomato/how-much-sun-do-tomato-plants-need.htm