Yup I did southbound, and I didn't feel any loss of excitement, since there was still Rockies to look forward to. And, southbound might be good in a way that you know that you have 7 days on the cruise to rest so you can just chiong all the way during the time in Alaska, then go on board, eat, sleep and rest
As for the distance to the glacier, I would say not as close as I could like to, cos big ships can't get that close. The smaller boats we took for Prince William Sound could get much closer. If I didn't remember wrongly, I had to use my wide angle to get most of the glacier in so it gives you a rough idea

Yup we took China Airlines, cheapest, with a stopover in Taipei.
Anchorage to Seward is around 200km and there're a number of stops along the way eg Potter Marsh, Beluga Point etc to see wildlife, so in the end we took at least 5 hours to get to Seward. From Anchorage to Whittier should be 120km so if you drive non-stop, should be at most 1.5-2 hours. That time, I think many people reached Whittier in the morning for the 6 hour cruise, and then got back in time to check into the big cruise.
Rockies is another huge area for phototaking. Too many I would say

If you want to cut down on Rockies, you could just visit the more famous places eg Lake Louise, Banff, Jasper etc and leave the rest for next time. For Alaska you could plan for more time to go up all the way to Denali for a few days, then go south to Seward, then to Whittier. For a relatively relaxing trip, maybe around 10 days in total?