Oh, you are asking a bunch of enablers here . Greyhound to greyhound introductions usually go very well as ex-racers have been used to being around other greys all their lives. Its best to take your current dog along and let him "pick out" his new friend if possible. If you do that and he shows no preference, then take whoever you like. I had my first grey as an only dog for about 6 months and after that I always had multiples, either my own or fosters, and never had any problems. You should still keep an eye on the at first, muzzle or crate them when you aren't around, because even if they get along, at first there can be squabbles as they sort things out. for how long? It depends, and you will know by watching the dogs, probably only a couple of weeks.
Go for it!