So the plan is to start out with a small number of chickens to give ourselves time to get the hang of things and make sure it's a good fit. That being said, I'd like to have a rooster, from the point of view of having a more natual environment for the chickens, and for the 'full experience' for ourselves. I see that chickens near us tend to be sold as breeding trios or quads - is it reasonable to expect that one such set would be ok, or would you normally get extra hens in addition so that there's a better male/female ratio?
Also about coop design - we were able to get a large disassembled garden shed for free which I want to repurpose since I learned that the pre-made coops they sell are probably much too small for the chickens to live naturally. I'm thinking of rebuilding it more or less in the same shed shape, but elevated about a foot and a half off the ground and filling in the gap at the bottom with wire mesh. The idea being that it would give plenty of ventilation but the draft would be low down so not blowing on them while they're roosting. We're in Ireland so the temperatures are very moderate, does that sound like a workable idea?
And last question (for now!) we have a lot of different kinds of weeds in the field where we would plan to let them free range. I get that in general they should be smart enough to not eat dangerous things as long as they have other options, but some of the weeds are quite a high proportion of the greenery in that area, such as horsetail and buttercups. There is also a decent amount of grass and clover, but I'm wondering if we should be thinking about clearing and re-planting the area, or am I just overthinking this?
To anyone who made it this far through my post, thanks, and I appreciate any tips you can give!
I'm glad you're taking the time to think this through, and developing your plan BEFORE you get your birds!
Roosters can add a new dimension to flock keeping, but they also require some extra considerations: If you start with chicks, and there is a cockrel in the mix, he is more likely to be aggressive to his flock mates b/c he's not had anyone to school him in proper dating etiquette. He will mature faster than his pullet flock mates, so will harass them unmercifully. I would recommend that you get pullets, and wait until they ALL are laying, and THEN, add a rooster (mature male) who has a proven track record of being gentle with his harem. OR, you might consider adding a cockrel to a flock of hens who are entering their second laying season. Older hens won't take any guff from a cockrel, and will trounce him every time he lets his hormones do his thinking for him.
As for your garden shed, what are the dimensions? The general recommendation is for a minimum of 4 sq. ft. in the coop per bird, and a minimum of 10 sq. ft. in the run per bird. I like the idea of elevating it. but, you might want to make it about 2' above grade. That will make it easier to manage if you need to get under it for any reason. I would leave that area open to provide shade for your flock. My birds LOVE hanging out under their coop. It's blocked off now, b/c I have not been able to put netting over their summer run, and we have huge hawk predation issues. But, if you do allow access for your flock under the coop, make sure you can reach under there one way or an other. I can reach under mine with a rake. Occasionally, some one will drop an egg under there.
As for your field with buttercups and horse tails, depending on your source, they are edible, or they are not! If the birds have access to all of the greenery in the field, they should be fine. My birds skeletonize the rhubarb leaves (which all sources state are poisonous) in my garden every fall. I would not choose to put poisonous plants into a chicken run where the birds do not get to pick and choose what greenery they eat, but in an open, free range situation, they should be fine.
Check out Henderson's chicken chart for a nice list of breeds you might consider. When you've chosen a few breeds that interest you, then start doing some more detailed reading. There are threads specific to most breeds here on BYC.
http://www.sagehenfarmlodi.com/chooks/chooks.html
The coldest I've ever experienced was -6... 
So, I messaged a friend of mine and we went to get 4 mixed chicks from her. Three of them have air pockets on their shoulders when they eat, so I went to the feed store and picked up 4 more. Just in case. 
