For bar scene, O St is generally a college aged crowd. It can be fun if that’s what you want, but I’d say stick to the Haymarket area. Leadbelly’s and Lazlo’s are probably my favorite restaurants down there. For Haymarket bars I’d recommend N Zone, Tavern on the Square, McKinney’s, Kinkaider Brewery and Bierhaus Maisschaler. The Railyard with Gate 25 and Longwell’s is a popular spot too. There’s also a cool vintage clothing store in the Haymarket called “Great Plains Vintage.” They have plenty of Husker stuff but have all kinds of other pro and college team stuff too.
For tailgating there’s places all over. If you’re in the Haymarket area you can easily access a bunch in the parking lots behind Pinnacle Bank Arena and into the Baseball/Softball stadiums. Roam around and mix it up with locals. Let em know you’re from out of town and it’s your first Neb game. You’ll get plenty of folks offering food and drinks.
For the Game, I’d say avoid South Stadium if you can. It’s not bad, I just think other parts of the stadium are more user friendly. I’m partial to sitting in North Stadium. Since it sounds like you just generally appreciate college football, I’d say get to your seats early enough to catch the pregame stuff with the band and so you can see the tunnel walk.