What sprockets are you looking at? Technobots list the weight of their products underneath the part number so you should be able to look there, see the weight and roughly work out how heavy your drive system would be.

For featherweights, you'll want to be looking at the 6mm or 8mm sprocket sizes. I'm not sure what size 4 4 Toon uses, but as an example, I think DB5 uses the 6mm size and they have been very reliable. And for an average guide, a 40-tooth sprocket from the 6mm range weighs 144g, which isn't too heavy.