I agree that most of your shooting will be wide angle.
I live in Flagstaff, about 75 miles from the Canyon. Being used to 7000' makes a big difference in how well you will tolerate the altitude. If you have any chance to practice at high elevation, do it and see how you fare. Your two-day round trip may be rather optimistic.
For a February trip, you should be prepared for the possibility of a
LOT of snow. A storm that dumps as much as 2 feet of snow at the south rim would not be surprising. In January 2010, we had 4.5 feet in the course of 3 or 4 days of non-stop snow. See some pictures at
The Big Snow of 2010 (taken with my K20D). (If you want something hotter, check out the fires about 5 months later:
Flagstaff Fires 2010 .)