Congrats on the upcoming adoption! Greyhounds are such fantastic dogs (although most of us around here tend to be pretty biased ). And good for you for putting so much thought into this ahead of time.
I have three greyhounds now and with all of them, I've initially tried to limit their time between bathroom breaks to around four hours. Eventually, he/she should be able to go much longer if needed (my hounds can go up to nine or ten hours at a pinch, although I don't do that to them unless I absolutely HAVE to). Mine all came straight from the track or kennel, though, so it may be different for a hound who comes from a foster home.
As for the separation anxiety, you should do a search on this board for "alone training." Taking the time initially to ease them into it is definitely worthwhile. Kongs are a GREAT help with a lot of hounds. Put in a little food in - kibble, yogurt, pumpkin, dog biscuits, peanut butter, whatever you have on hand - and freeze them. Give the Kongs only when the dog is in the crate. I think my hounds actually look forward to my leaving sometimes.
Good luck with your adoption. Greytalk is a wonderful resource. We'd LOVE to see photos once you have your hound home.