I just wanted to comment on the age difference thing.
All four of my dogs are 2 years apart. Ozzy is 7, Enzo is 5, Indy is 3 and Jones is about to be one.
You really have to factor in breed life expectancy, and I was fairly certain grey's live a long time, so it's a possibility that they'll all end up old together, which can definitely be hard.
With my guys, it's hard to tell. Going by Ozzy's breeds and general hardiness, I would be comfortable saying he could make it to his late teens barring any unforeseen accidents or things like cancer. Going strictly by Enzo's breed, she may make it to mid teens. She may make it later simply because of keeping her fit and active. Indy, I'm fairly certain barring cancer will make it to mid teens, and Jones as well. But that gives me a two year gap in between each dog being "really really old"
Of course, they could all "senior" near the same time, but I feel comfortable with a two year gap enough that it doesn't bother me too much.