Welcome Drew - I am not an expert but do enjoy my chickens. I would guess you could have 4 - 6 comfortably depending if you go for Bantams or larger types in the space, especially since you say they will be let out sometimes as well. I think the smaller type would probably suit you better in these circumstances. Even go as far as searching out some of the specials, which you would have to pay more for, but I personally think would be worth it. If you only have a small number, why not spash out and buy a selection that will light up your garden.
Have a look at some of the Bantam websites - you would be surprised just how small you can get them. Silkies, Golden Partridge, Frizzels, Miniture Buff Orpingtons, Japanese, are just some of the ones that we have that are so lovely, friendly and full of character, but quite compact.
Google miniture Bantams - you will find a selection of the smaller types I have mentioned, which obviously lay small eggs. Then google Medium Bantams and you will find the selection there that lay medium eggs.
Your normal Bantams can acutally grow quite big in comparison to the ones I have just mentioned.
Good luck with your search and let us know what you decide.
Here is a website I found which you may find useful just for general information.
http://www.freewebs.com/professorchicken/Kate
