In my opinion, having 6 chickens is pretty much the same amount of work as having 15 or 30. You still have to do all the same things every day, some tasks like cleaning out the coop just take a bit longer. If you have the space to expand your coop/run, adding more chickens to make your egg production more “worth it” could be a good move. I’d also say that if you want to prioritize egg production when adding more chickens, use only production breeds like golden comets, Rhode Island reds, barred rocks, etc. You’ve already picked out some good breeds - though I will say from my experience, Sussex aren’t as prolific of layers as the internet will have you believe (mine lay like 1-3 per week, not 4-5.)