I would pick Potwisha over South Fork--much closer to the GIant Forest area. Even then, maybe consider Lodgepole if you are OK with colder conditions and some snow.
I would definitely spend a day walking through the Giant Forest. A loop that I like: park near Beetle Rock, then follow the Crescent Meadow Road towards the meadow itself. You can check out Moro Rock along the way, but I suspect it will be too icy, especially without micro-spikes. From Crescent Meadow, head to Eagle View, especially if you didn't do Moro--nice views of the Great Western Divide. The trail to Eagle View (the High SIerra Trail) will probably be snow-free, but Eagle has the best views for several miles. Backtrack, then take the Trail of the Sequoias back to the Congress Grove/McKinley junction area. Follow the Alta Trail back to Round Meadow, then take the spur to Sunset Rock before returning to your car. You might be able to park at the roadside parking lot to see the Sherman Tree, depending on if the shuttle is running and/or the new parking lot is open.
I did this loop back in late-ish February and snowshoes were not needed. You will probably be able to follow the summer trails instead of the marked winter route. There is probably less snow now, although a storm is coming in later this week--but it looks like it will be dry.
Sledding in Wolverton is also fun, but I don't know how much snow will be left.
If you do stay at Potwisha, another good hike is to head up the Kaweah River from Hospital Rock or Buckeye Flat (if open). There is a nice creek/cascade right after the summer trailhead, and a few more miles in Panther Creek has a nice cascade and some good pools. I'd turn back here--Mehrten and Buck Creeks are not quite as nice. There will be no snow along this trail, but beware of poison oak and rattlesnakes.
As for the Redwood Canyon trail, I saw vehicle tracks heading along it, so I don't know if it's closed or just not plowed.