Yeah, most people do base camp close enough to summit and return in one day, but most of those people have summited many smaller mountains before too...
Do you know what route you'd be taking? Would you be hiring a guide? The guide thing is only really needed for the mountaineer's route, I think.
Definitely start training. You can hike the same distance here in a day and not even feel tired, but things are different 14,000 feet up

I'm down for some smaller local training trips though