Looking to hike some--St Helens? Cascades? Lassen?--the first/second weeks of October. What should I expect for conditions?

Check back on September 30. No way to tell right now. Could be sunny and nice, could be under a couple feet of snow. That's prime iffy time right there for OR and WA. In general though, you should still be able to do St. Helens at least. But be prepared for full-on winter as well as 70 and sunny. Check the NOAA forecasts for places around the Cascades to pick the best areas and call the local ranger stations beforehand to check.

Good luck. Hope you get to sneak a couple peaks in.