There is no problem whatsoever in leaving an adult dog alone all day, and if you have them from a pup they'll easily get use to it.
We got our Working Cocker (see prev post/picture) at 8 weeks old (June), we had a weeks holidays and then my wife came home lunchtimes for the next few weeks. He was alone mornings and afternoons. Then summer hols where he was left odd days.
We started with a pen (1m x 1m) with a cover, and under-cover. We then bought a full size walk-in cage (3m x 2m) with an insulated kennel inside. He spends days in here, and sleeps inside.
He has plenty of toys and is often walked by neighbours, plus obviously us and a weekly bike run. He also travels well.
I would totally recommend one, and they're good with kids too.