BHWT will tell you if they have been wormed or not. Start with layer mash mixed with a little layer pellets - they don't recognise layer pellets as food 'cos they only get mash in the intensive farm. Then gradually increase percentage of pellets - we have found they get used to it pretty quickly. We had a girl with a prolapse from our most recent lot, first time we had experienced this - look out for a messy, protruding bottom and sticky feathers - if this should happen there is lots of advice on here and other sites of how to deal with it.
We also put some poultry tonic in their water for the first few days to help build them up. They won't 'know' they have to go to bed at dusk so will need putting into the hen house for the first few days - took ours about a week to get completely used to the idea.
Useful to rub all perches and especially nooks and crannies with mite powder to prevent infestation in the first place. Also, totally clean out and allow house to dry weekly.
We use builders sand on the floor of our house - makes cleaning daily droppings easy as it's like scooping up from a cat litter tray!
I'm sure there will be others along with other advice too - this is just what we have found from keeping rescued hens.
Donna