I activated this summit a few years ago, so doing this write up based on the best of memory.
Back then you did not need a permit for day hiking or staying overnight in the Three Sisters Wilderness. Today you will need to apply for an overnight permit if you are camping, as well as a day hike permit for certain trail heads. See the following link https://www.recreation.gov/permits/4675311 for info on how to obtain a Central Cascades Wilderness permit, as well as this map
showing the current trail heads that require a permit and trail heads that have free self issue permits at the trail head.
I started my hike at the Devils Lake/South Sister trail head, though other trail heads in the area will work too, some may just add mileage to your trip. Hike to the Wickiup plains area on trail 2000 and once you feel like you are ready to go off trail, start heading towards the summit. It is a steep climb up in certain sections and there was some thick bushwhacking at times at the base of the summit. I just headed off trail and just looked for the path of least resistance.
Once on top, there is some room for an HF antenna, but can get crowded if you are bringing company. Be careful as there are cliffs at the summit from what I remember. One step can be land and a rushed summit fever got to get activating SOTA step can be sky, so be mindful of where you are walking and take it slow.
AI7NN