There are several options to hike a circuit around Glacier Peak, between 80 and 100 miles, depending on route and side trips. Resupply would be challenging as there are no towns near the trails. I’ve only been on the PCT and the North Fork Sauk Trail in that region, but here are a few options based on your preferences:
3/4 circuit from Buck Creek to Cady Ridge:
All on fairly well maintained and well-traveled trails, although the first 2 miles or so of Cady Ridge trail is supposedly steep and a little rough. You’d be coming down Cady Ridge at the end of trip with light pack by hiking this semi-loop CCW starting at Buck Creek. This semi loop would require a short car shuttle or some hitchhiking on less frequently traveled dirt roads.
Full circuit out of Buck Creek:
All the way around Glacier Peak, but uses some poorly maintained trails with no recent maintenance (either the upper White River trail, or the Indian Creek trail in particular). There are also a few more rougher trails (W side of Little Giant Pass, N side of Boulder Pass). And there would also be a crossing of the Chiwawa River, which is best crossed in mornings for lower flow, although Aug to Sep will have less flow anyway. As with the first option above, hiking CCW has you on the roughest trails toward the end of the trip with light pack.
For any loop route, you could add a side trip to Image Lake (classic view of Glacier Peak reflected in lake) or lengthen the trip by going over Spider Gap and Cloudy Pass via Lyman Lake (some easy off trail).
The PCT in this section is good but does have lots of vertical gain and loss. Same looks true for the other trails used to complete a loop or semi-loop (Not unlike Wonderland Trail). Best to be in strong physical condition, or shorten your anticipated daily mileage accordingly. If you’re interested, I can send you some KML files for Google Earth showing various options.