Good idea researching before you head up, hopefully you have at least a week to explore. I've spent the last few summers up there working and will likely be up there again this year. My experience is limited due to only having a few days off but I'll offer up what I can.
Your timing is good, you'll find a chart in this link that shows you prime times and availability for different species
http://www.noelgyger.ca/. The website is a great resource for that area and has up to date fishing reports, but I would take them with a grain of salt. Explore rivers even if the rivers don't sound like they're fishing well, you may be surprised. I didn't fish the Skeena much, with my limited time it was difficult to find suitable bars conducive to fly fishing without a boat. You could always try ferry island if you don't mind crowds. I mostly fished the Copper, Kalum and Kitimat Rivers all great for walk and wade fly fishing. The Kalum and Kitimat River will be great for salmon fishing during that time if you're interested in pinks, chum and coho. If your focus is on steelhead it may be best to concentrate your efforts on the Copper at that time (again coming from someone with limited experience in that area). I had good success last August on the Copper for summer runs and coho. That river is a bit moody and tends to silt up a lot if it rains or warms up, but don't be put off by poor visibility. Below is a picture of a coho that hammered a 4" marabou tube fly on the retrieve with poor visibility.
If you're planning on exploring the Copper and other Skeena Tribs, it would probably be best to carry a radio programmed with the proper frequencies when you head up. The roads will be busy that time of year. You can rent them for cheap at Coast Mountain Wireless in town.
Good luck and we may cross paths up there.