"2) Is there any advantage to doing a North vs South bound route? The main difference seems to be related to times of arrival/departure from ports and College Fjord (Scenic Cruising), Alaska vs Hubbard Glacier (Scenic Cruising), Alaska"
We just disembarked today from the Northbound on Majestic.
I have not heard anyone making the distinction between the schedule of the 7 days; but there is a nuance to be known. On the Northbound you do Glacier Bay and the College Fjord at the "end" of the cruise and we really liked the culmination of our cruise that way.
At first, we were regretting not doing the land in Alaska first and then the cruise Southbound. We like the cruise so much that we want to do it again. And as we are now looking to book I am still leaning towards the Northbound due to the way it is set as a 7 day cruise. It starts with the 3 ports in the first few days and the Scenic part towards the end. Also the food seemed to progress in quality towards the end, when they served escargot, lobster, and other higher end dishes in the Allegro and Concerto (standard dining). If you plan on using specialty dining, try to find the menu for the week and avoid scheduling your specialty dining on the nights when the (standard dining) has a better menu.
For your information we did Glacier Bay in the late morning and during lunch time.
We did the College Fjord later in the day (the day before ending the cruise) end got to Harvard Glacier which appears to be the biggest glacier in the College Fjord right around 6:45pm, and we stayed until 7:45pm. (This information is useful when planning your dinner), because you really want to plan on being able to enjoy the view. And even the few hours before 6:45 we were watching other glaciers and wild life in the College Fjord area.
That is information that I was not aware of, and I think you should try to plan for prioritizing the view and wild life watching; and schedule your meals and dinner accordingly. Find out what are the hours for breakfast, lunch, and dinner at each venue.
If you plan on visiting the Skagway we find Yukon Discovery Tour very good, because you get to experience the same views as the railroad, and be able to travel farther, into Yukon Canada.