Oh dear.... where should I start?
Even with a good safe area to leave a pup... it will ruin at least one thing that you love during it's first year if you take your eyes off it for two minutes....
I would adopt an adult if you really have to leave it all day. The first six-months of a dog raising are REALLY not worth the aaaawwww of having a puppy.
All large breeds have some incidence of bad hips, but you are also taking on known hips in an adult. You know by the time they are two whether they are going to be OK.
Well, yes and no. Some breeds are less prone than others - hip dysplasia in collies (for example) is virtually non-existent. Of course, collies can have eye problems, so there's always a trade-off :(
Proud owner of a 6 month old rough-coated collie ;)