Hi Sean and welcome to Cruise Chat.
You're in for a spectacular first-time cruise experience, going on Celebrity to Alaska. Be prepared to get hooked on cruising.
Did you also look into taking advantage of Celebrity's transfer from Anchorage to Seward? The bus usually makes a stop along the way, at Portage Glacier or similar, for a boat ride out to the glacier. I don't recall the latest arrival time to take advantage of the cruise line's transfer, or if price was a determining factor in your decision to drive yourself. But that's another option, if still available. Of course, driving your own car gives you flexibility you won't have on a transfer bus.