More hens?

We started keeping chooks 2 years ago and have 2 wyandottes and a barnebar.  So far they've lived in a metre square coop with a 1m x 2.5 m run.  We've let them free range all day but a couple of months ago we had a visit from Mr Fox.  Thanks to my husband's quick intervention the girls were saved but we decided that to keep them safe their freedom of the garden would have to be curtailed.

My husband has made a 9ft x 9ft covered run on a 10ft x 10ft slabbed base and attached it to the side of a 6ft x 4ft shed that he's converted into a coop for them.  We've covered the slabs in bark chippings, added some perches and a large shallow box of earth.

We live near to a chicken farm that's closing down at the end of this month and we've got the opportunity to have some of the ex -batteries before they go to slaughter.  If we do have some more then it'll have to be 3 to give them a chance of integrating with our girls but I'm worried that putting 6 large hens in the new run will make it overcrowded.

Any opinions?