The one thing to do that isn't a panel? How about 6
1. Cosplay, take pictures of cosplayers/have your picture taken, go to a photo shoot of a favorite anime/video game/movie, chat with cosplayers and learn new skills, hug a favorite character
2. Video games they have a whole area you can play em and have contests. Last years Street Fighter was fun, someone played F.A.N.G and no one knew what to do with him as he isn't played because of how low he is. Was super fun to watch, laugh and chat with other players. They even had a working DDR machine and Karaoke with a stage
3. Board games another area FULL of board games with LOTS of players happy to play with you and or teach you how to play.
4. Get Autographs of from favorite stars
5. Merchant Booths its easy to spend hours in there while debating on if you really need that epic shirt. Also gives ya a reason to buy a mystery bag and take what you don't want to the swap meet. I've gotten some nice stuff that way, just last year got a cool Eevee plush.
6. Artist Ally I LOVE going there, seeing what art they come up with for favorite characters and shows, its one of a kind art. I got a great pokemon sushi poster I love that my sushi chief wants a copy of for his restaurant.
Also the video games and board game area are kept open after midnight for events and night owls.
Don't know anything about the Double Tree. You can always look up online reviews, sometimes they help.
As commented before me there is food in the convention center, its pricey and some of it was ok. The nachos made one of my group sick. But they had pizza, salted/chocolate covered nuts and ice cream that was good. There is a Dennys, Burger Vill and Red Robbin like a block away. I cant remember the name but there was this little place about a block away from the motel 6 heading away from the convention center, was nice good teriyaki chicken and quesadilla with chips. If your a picky eater its kinda hard but its portland so its all good. I went out for sushi and VooDoo Donuts
When they release the scheduled in Oct you will be able to see all the stuff and plan what to do when. I'm sure you wont have a bored moment.