Border collie question?

I want a dog... i have a yard but i have 3 cats too. I want a medium size dog. I read that border collies were recently ranked as one of the smartest. How would the dog be if i worked 3 day s a week long hours( nurses hours). Husband would be able to spend most of morning and noon with dog on those 3 days but dog would be alone til nine in the evening... are they overtly full of energy...i would walk them once/twice a day and take them to the lake and out to play alot... suggestions?