I don't really use the scripting but it's clear that you should learn how to use Construct 3 a bit first. I think this would be normal even if you are a javascript programmer coming to use Construct 3 because it has its own way of doing things.
To create a grid of sprites you could use a nested for loop that creates sprite instances at positions that you then add to the X and Y on each iteration of the loop. Or you could build the grid in the editor from a sprite that can be invisible and then create your objects on top of that using events.
If you mean hundreds of different objects then yes you need to add them, or you can have one sprite with the different animations depending on what type of game it is and if that's useful.