If you hike alone in Denali, stick to the open tundra areas. Highway Pass and the area between the Stony Overlook (mile 61) and Eielson Visitor Center (mile 66) are great options. Make noise (I clap my hands and talk or sing to myself out loud). The key is to not surprise a bear. But they are not hanging around every bush ready to attack!
Yes, I often use Wonder Lake Campground as my 'base' for Denali NP. I enjoy the wildlife (esp bears) and hiking in the west side of the park so it greatly reduces the 'transit time' vs. staying at Tek or further east. You can reserve the Disco hikes only 2 days in advance. Check when you arrive at the Visitor Center for availability and to reserve for the first couple of days. Otherwise you can reserve them at the Eielson VC.
Seward has Mt. Marathon, which those in good shape (or idiots!) run up and down on July 4th for fun. I haven't done this hike but it is supposed to be great for the views. I have done the Harding Icefield Trail hike at Exit Glacier. Strenuous but excellent. It is a formal trail almost all the way. You will probably encounter some snow at the top. I have also hiked to/near Caines Head. Last year I hiked from Lowell Point to Caines Head and before the hike I had arranged a water taxi to take us back to Lowell Point. Next time I might take the water taxi round trip to Caines Head since there are a lot of trails in that area that we didn't have the time or energy for. There is also the easy path along the waterfront from near the Holiday Inn to the Sealife Center.