Damn!! That's a lot of driving. 4 or 5 days in Colorado is kinda of tough, you couldn't do all the skiing or hiking in CO in 4 or 5 years, so that being said. You need to be aware if you are going to be doing any backcountry that you really need to get an early start, usually you'll want to start skiing no more than 2 or 3 hours after sunrise, depending on slope aspect, to avoid wet slides and if you are hiking you need to be off the mountain around 2pm, to avoid lightning. It sounds like your trip is going to be more like 4 or 5 hours driving get to a place and hang out which will make pursuing any backcountry adventures somewhat problematic.
I'd recommend driving to Crested Butte after skiing A-Basin, spend two days in CB, there are lot's of bc opportunities around there, then drive to Ouray (beautiful) or Telluride (never been) spend a day or two there.