I think of their need for space in terms of concentric circles, for the first few days they eat, drink and sleep in the warmth of protection of either a mother, a mother heating pad set up or a heat lamp, all within a few feet of one another. depending on how cold it is, they will venture a little further out as they age, sometimes if it's warm enough they will spread out more quickly. you can gauge how much room they need by their behavior and outside temp. there is no need to keep them inside your house early on, just make sure they have figured out the ins and outs of staying warm and finding the food/water. the other thing to look out for, particularly if you are starting a large flock, is making sure they have the ability to get away from the heat and if need be, get away from each other. if they are too close together, behavioral problems are more likely to crop up, feather pecking and such. for a group of 30 plus chicks, I like to have a good 5'x5' area for them to run around, it's plenty of room to keep the bad actors from picking on a stragglers so much. I would cut off access to the run for the first couple of weeks to assure they don't get lost "out there" and forget where to go to warm up. when they get cold they start to shut down and sometimes don't do the obvious, if you seem one hanging out in the cold just standing there with it's eyes closed, probably a good idea to place it in the warm area, especially if it's out of direct line of sight from the brooding area.
mostly the chicks just regulate themselves pretty well as long as they don't get sick or cold and you'll get a feel for how much room is good. within a few weeks they start to feather out and become much more independent and able to wonder further from the food and heat safely.