Thanks for the replies Ol Grey Mare and donrae. We'd be getting them from the local hatcher supply so maybe there won't be the size difference I'm worried about. I'm sure we'll learn to appreciate their individual personalities soon enough!
Let me elaborate on the space bit - one of the difficulties I found was that unless you're willing to spend ~$600 or more, it's pretty hard to get a decently reviewed pre-fab coop that has adequate space for anything above 2 chickens (at least according to the guidelines on byc and most other reputable places). I'm almost certainly going to attach another section into the pre-fab coop to extend their sleeping space. I think I'm going to probably put together my own coop in a couple years, but for right now I might just extend the pre-fab we have. We live in Southern Maryland, so we get cold winters and hot summers. I explained my plans for their coop and run in another post - so I'll copy it here and definitely appreciate feedback:
I'm planning on having separate caged in coop and run areas for 4 chickens. Both the coop area and run area would be simple structures using ptl and hardware cloth. We have plenty of predators in the rural area we live in and I don't trust the simple pre-fab coop I'll be using initially to protect the chickens from foxes, raccoons and hawks. The plan is to take the chickens out of the coop area in the morning and put them in the enclosed backyard run area until dusk when I'd bring them back in for the night. The backyard run will be 4'x8' and I plan to be able to move it around our yard every couple weeks so they get some new territory to peck at and so they help us fertilize the backyard! I've been lurking on BYC for a while and think I have this part somewhat figured out as the hardware cloth enclosure and a 2' apron should be sufficient to keep them safe (though if anyone has other recs, I'm all ears!). Part of the backyard run will have a roof and will have an enclosed space as well in case its too windy/chilly.
We have a large raised deck in our back yard above a ground level area that has loose stone for the flooring (I've already put on a waterproofed plywood floor on paver sand as a base). There's a door that leads directly from the garage through the back to this sub-deck area. My current plan is to put a 4'x8' frame enclosed with hardware cloth around the pre-fab coop I bought (http://www.hayneedle.com/product/boomerandgeorgetreetopschickencoop1.cfm) underneath the deck. I realize this sounds like overkill but my wife insists her chicken babies be inside fort knox and I think the location will help protect them from the elements/insulate them a little. Based on the replies and the space concerns, I'm thinking about doing away with the small run the pre-fab coop comes with. That way I can add more floor space to the coop and the chickens can still wander the area around the coop on days when the weather is too poor to let them out into the backyard run.