I'm dealing with some of the same questions. I purchased my first 8 chicks in June of 2011. I lost one that October to a bobcat about a month before the flock started laying. I added two Easter Egger chicks during the winter (having found a nice lady on Craigs list who was raising a few more than she really needed). Summer of 2012 I purchased 35 Freedom Ranger chicks to raise for meat. Ended up keeping two of the pullets and one of the cockrels. In the meantime, I lost two more of the original 8, one to sour croup and one...not really sure, but I think it had to do with the stress of having to evacuate from our home due to the Waldo Canyon fire during the hottest summer on record. So, long story short...now have 10 chickens ranging from 6 months to 18 months. This is honestly about the maximum comfortable occupancy of my coop.
My two 18 month old Wellsummers stopped laying almost entirely this fall when they hit their first moult, and although they are back to fully feathered, I get maybe 1 Wellsummer egg a week from the two of them. The 18 month old Barred rocks egg production is decreased from last year, but pretty reliable, as is the White Rocks. Easter Eggers are going strong at about 12 months of age and the Freedom Rangers...well, laying pretty well, but not as reliably as the others were at this age. I've ordered 8 more chicks from MPC for delivery in the spring (7 being the minimum I can order here). I figure that in the summer of 2013, the Wellsummers will be retired to the crock pot, as will the three Freedom Rangers (they just eat more than the others, lay less, and take up needed space in my coop). So that's five I'm mentally preparing myself to "do in". I don't know about the rest. I'm figuring I can offer several of the new chicks as "started pullets" on Craigs List if my remaining hens are still producing well into their second year. I'm kind of fond of the Rocks and the EEs. We'll see, I have time.