Five week old chicks

Hello everyone,
I collected some five week old chicks (at what age are they pullets?) yesterday. They are off heat although I brought them in last night as the temperature dropped significantly.

I have set up a separate run for them but how much space should each one have at this age?

I was warned that this hobby is addictive and with the purchase of an Eglu cube with walk in run and extension, and now a second small Eglu and run from eBay, I feel i now have the most expensive eggs in the county! However as I have severe arthritis I have found the Cube and WIR so easy to manage with the added benefit of no red mite ( touch wood/ plastic?)
Many thanks,
Jane