DannyBoy, I think the best thing to do is to look up your nearest BHWT coordinator (via their site), and ring them and have a chat. You would need to talk them anyway to register, they have to sus you out before you can adopt.
As I mentioned mine have been relatively trouble free.
Providing you get birds that don't arrive with injuries, the first thing they have to deal with is the trauma of rehoming. But to be honest, as long as you are aware of what they are going through, and keep an eye out for problems, they will do the job themselves.
For some it can all be too much, and they just give in and pass quietly, and there is not a thing you can do. My experience was sheer joy. When they emerge into the sunlight and start doing chicken things, its the best feeling in the world. Book time off work, cos you won't want to leave them!
When you first get them, they'll need to overnight in the dark in the coop, and then just let them out to mix with the others and see how it goes on. Remember, they won't have been in the same cages, so will be strangers to each other too. There will be some re-establishment of the pecking order as they join the flock, but that's the same with any new chooks. Don't assume they will take the lower order either. The balder, the fiestier!
Depending on what they've been used to, they may need to be fed mash for a while, but they soon get used to pellets, and corn, and worms, yum!
They might be well feathered, they might not. Some of mine were tatty but fairly well covered, but poor Tilly just had a few quills and a bright pink bare bum for a full 12 months. All through that dreadful winter, I had a chux tux on standbay
But she got through on her own. She is now fully feathered and magnificant. I'm going to post a pic of her when I get round to taking it. I'm so proud
The main problem I've had is to do with shell quality, and it's because they are coming to the end of the reliable egg laying life. That's why they've been thrown out.
We've had lots of soft shell eggs, which can be awful for them to lay, and some broken shells. Have had to extract broken eggs a few times, which was a bit of a trauma for them and me. Stiff drink and a lie down afterwards
But then again, those are problems that will come to most chooks eventually?
BHWT will provide all the advice and information you need. Why don't you give them a ring? Have a look at the before and after, and see what you're missing.