We have had our hound for just over a year now.
Like you, I waited until DS4 was 5 and I am glad I did.
We fostered a grey first, to get an idea without the immediate commitment (I mainly had to let DH see that this was not an insane idea) and again, I am glad we did, because it mainly taught me that sighthounds are first and foremost dogs, and then greys. By which I mean if you have dog experience you will only adjust yourself a little to figure out what to do with a grey - although it has been a learning process.
Ours was only 20 months old when he came to us, never raced because he was 'too playful', read 'absolutely bonkers'
Yes, he lies around and sleeps a lot, but he can also jump higher than me at the sight of a lead being pick up or me putting my shoes on…
He IS a big dog - I had thought I'd thought about everything that entailed and was fully prepared for the cost of foot/insurance/jackets/space in the car etc etc, but had not really allowed myself to consider that big dog + lots of food = lots of poos… I've got over that now.
He is good with the kids (I have 4).
He gets grumpy in the evening and does not like anybody male standing 'over him' or near his bed at night - he gives v quiet warning growls, has never bared his teeth and we now know to just leave him alone.
He is wary of strange men, may growl and disappear.
He is good with other dogs, but had to learn that dogs come in all shapes and sizes. At the very start he picked up somebody's small white fluffy dog (Lhasa Apso type) and shook it - other dog was ok, other owner was exceptionally understanding, and I had learnt a very valuable lesson.
He will chase anything that runs away from him: cat, squirrel, dogs - dogs he wants to play with, but he comes on VERY fast which is of course perceived as threatening. I only let him off lead in a fenced field and with dogs of his size/weight, most of whom we now know. They are teaching him better doggy manners. In many ways he is like a rude teenager.
I still go to the monthly walk the charity he came from does and it is lovely company, for him and for me. I've made some new friends. A GH owner's club in the nearby city sometime rent a horse riding school arena for some indoor fun with lots of hounds.
I'd say go for it.
I am sorely tempted to get another grey, but I think we'd struggle for space.
And there'd be more poo….
Do lots of research.
Meet lots of greys.
Develop a relationship with a local charity you like - I visited a few and stuck to the one he came from because the foster ALL their dogs before rehoming them, so I felt we knew a little bit about him beyond just his parents' names and 'was bred for racing but never raced'.
I am very excited for you - good luck!