You'll likely be able to buy tickets from their box office online up until Gameday as I'd be pretty surprised if this game sells out. Visitor section is in the endzone with the large video scoreboard. Not terrible seats, but far from the best. Having been to lots of games at Autzen, I'd recommend sitting on the side of the stadium with the roof, probably about halfway up if you can find something decently priced. The September sun can be brutal if you are sitting on the uncovered side. Tailgating should be a good time and I'd also encourage anyone going to check out the indoor tailgate at the Mashofsky Center, which is their indoor practice facility that is right next to the stadium. I do believe they have the clear bag policy in effect as well as a no return policy if you leave the stadium, so once your inside, you're in for the game. FYI, the indoor tailgate is considered "inside" the stadium and does require a game ticket to get in.
The game itself should be interesting as Oregon has maybe the biggest offensive line in the country coming into the 2019 season, headlined by true sophomore Penei Sewell (6-6, 345, Frosh All-American). They also just signed the #1 overall recruit Kayvon Thibodeaux (D-end) who figures to play a prominent role, especially on passing downs. I think everyone knows who Justin Herbert is by now, so no explanation needed there.
One interesting aspect of this game is that the Griz won't have a ton of tape on the Ducks defense, with them having just hired Boise State D-Coordinator Any Avalos. This game will be a monumental test and might figure to be the toughest of the big time opponents we have faced maybe ever.
Post game, I'd highly recommend walking from the stadium to "The Cooler" for some beers as the traffic/parking situation will likely be a mess. Another awesome spot Montana fans will like is "The Beer Garden", which is essentially an indoor/outdoor version of Dram Shop but with 5-6 food trucks with various kinds of food.
If Sheldon High School has a game on Friday and you are there you might consider hitting that if you like high school football. Lots of former Griz players have come out of that school and it's still a place we recruit pretty heavily I think.