Hello,
Good luck greyhounds make loverly pets, although I've not rehomed greyhounds I have Beagles (I also show and breed) but a few basics help.
The greyhound trust are very good and should give you all you need to know but when you get him/her just let them settle and don't have everyone round to see the new addition it could make her nervous.
I'd expect a few accidents because of nerves/marking territory or if it's an ex racer living in kennels it won't know how to live indoors.
I'd imagine a weeks supply of food which gives enough time to find a brand you can easily get or what suits them, all my dogs are fed dry, better for the teeth easier to store, but it's down to personal choice.
Someone who has a rehomed greyhound is your best resources the previous post shows or just ring the greyhound trust up they'll always help (it's better to sort a problem than have to rehome). Or send me a PM me and the missis have spent a lot of time on animal instant and behaviour with spaniels and beagles and I'd be happy to help if your having a particular problem. I've also done a lot on dog food, a couple of mine had issues with various foods, bad behaviour/hyper/bad bowels so if your having issues with diet I can help there.