15 from day 1 sounds a bit much to me - I only started with hens last July and bought 4 POL for £15 a bird - Sussex, RIR, Bluebelle and Black Rock so I could tell the difference and enjoy the colours

The RIR lays the biggest eggs and is quite feisty in a nice way, the Sussex is top bird and can be a bit of a bully but is the quickest to "sit down" when I go in the pen so she's easiest to catch and handle. The Bluebelle and Black Rock are slightly more wary, the BB is quite nervous by comparison to the other 3.. but I love them all

Having got hooked I then took on 4 BHWT rescue hens in about September - all arrived bald but the upside was that by Christmas they were feathered and starting to lay just as the RIR went into moult. The other 3 haven't really moulted this winter but I have been getting 2-6 eggs through late December and January and never a day without at least 2.. By next winter I imagine I'll be lucky to get any of these laying, so the plan is to find another 4-6 POLs in spring and if more BHWTs come up in the autumn I'll think about a few of those as they're very rewarding to see the change in and even in one final laying year they'll more than pay for themselves.
My thinking is to bring in batches to keep production at a consistent level allowing for moults and retirement, but also so I can build egg sales before getting too many to cope with - there was a stage late last year where I was eating a 3 egg omelette for lunch every day as over December/holiday period there were no sales at all, folk being otherwise occupied and focused more on junk food than baking/eggs

The tactic also allowed me to test the waters of chicken keeping before inflicting myself on more than I could cope with cleaning out, feeding etc.
I had a foray into Araucanas and loved the hens, didn't get on with the cockerel so parted with them again

but while the eggs were lovely colours they were smaller and I found myself apologising to customers in some cases as the contrast to the huge RIR and BR eggs was noticeable.. I'm thinking Cream Legbar, Wyandotte, Maran as my phase 3 possibilities as I heard they were a bit less easygoing but will produce large and different coloured eggs aswell as adding more variety to my living room window view
