I'm not a big advocate for staggered hatches either, especially for newbie hatchers but it can be done. I wouldn' add eggs every week, because that will really screw things up humidity wise. I agree with PD. Having a second incubator is best. But, if you set eggs on the 15th, and really wanted to set more, I'd do it on the 22nd. That would put them a week apart. I'd run low humidity, monitoring air cell size for the incubation period, The first ones would be due the 5th and the second ones the 12th. As soon as the first ones hatch and you can get them in the bator, (I would not wait 2-3 days to move chicks) I'd get the humidity lowered right back down for the second ones till it's their time for lockdown. Just note, by doing staggered hatches in one bator, you have higher chances of having issues related to humidity.