Family companion and being left outside alone for 3 hours aren't really compatible. Most dogs tend to prefer one or the other.
I have a big hairy beast who loves to be outside as indoors is too warm for her but she'd hate it if the door was shut or I just left her there. Smaller dogs might struggle even with a heated kennel.
One of the problems is if someone comes on to your property, even with a legitimate reason - can you guarantee they would be safe or that they wouldn't let the dog out by mistake ?
If it's a dog suitable for being trained as an assistance dog, have you thought about speaking to the relevant charities and asking them about why they choose the breeds they do ? I appreciate that you don't necessarily need an assistance dog at the moment but they probably have better insight into what you could be looking at to get DC used to dog ownership .
How about visiting Discover Dogs to speak to breeders and get an idea for what you'd like. If I were you, I think I'd seriously consider a poodle as they come in different sizes, are intelligent, low shedding but they might be too high energy and I know the grooming can put some off. I met one at the beach and was amazed by how wonderful it was with its autistic owner and yet wouldn't have considered one myself.
And given that you've posted in the Doghouse, I'll throw in the idea of a greyhound - I know they are large but they tend to be clean, curl up small, and could cope with your walks without being on the go constantly. Not hairy. They would be better off inside however.