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I was waiting for someone more knowledgable to chime in, but it looks like I'm all you've got.

Trails in big snow years may still be quite deep. It's unlikely you'll need snowshoes or traction to get into Wallface, especially given the lean start we've had to this winter. Still, check trail conditions before heading in. Be ready for some snow and ice on the approach, at least in shady spots.

Weather can vary dramatically, as you noted. The last two Mays I happened to head up when the highs were around 80. Typical temps for a sunny day is a low of about 35 and a high around 65.

Wallface doesn't seep as much as some other cliffs in the Daks. Combined with the pretty good sun it gets (especially Diagonal), it'll probably be quite dry. Be ready for wet streaks down low, and the shady final two pitches are likely to hold some water. I did Diagonal in November, with lows in the 20s, and very little ice or water fell on us as the day warmed.

So, in conclusion - as long as you have sun for the climb (and hopefully a couple days before), you'll be just fine.