1. The dpad isn't great and I don't think it's good for fighting games. It's serviceable.
2. Loading times are OK. You don't notice any real difference vs the SSD in the 256 and 512 models. As I understand it, the 64gb models SSD isn't as fast. The Deck only supports UHS-I speeds, so you don't need to have a super fast card. I'd still get a UHS-II V60 card though as the download speeds are faster.
3. Deus Ex and Thief both work fine. Thief runs best when Proton is set to Experimental, but that's not an issue. Not sure about EAX support.
4. Framerates depend on the game. Games like Doom 2016 and Eternal will run on high settings at 60fps, I usually set games to 40hz anyway as it feels smoother than 30 and either extends the battery life or allows you to run games at higher settings. I'm running The Ascent at almost max settings and 40fps, DMC5 at close to max settings and 60fps, RE2 on high at 40fps, Wolfenstein New Order on max settings at 60fps (this game doesn't like being locked to 40), MK11 max settings and 60fps, Arkham Knight at max settings and 40fps etc etc..
Basically you'll be able to play games at settings that look better than PS4/Xbox One at equal or higher framerates. You can set mesh and texture quality as high as you like, only having to concede on volumetric effects, particle effects, or shadow quality in some games to keep the framerate locked. Obviously it varies by game, but regardless, you won't be disappointed with the performance.
5. I think so. It's certainly smoother than 30. I'd say it feels closer to 60 than 30 but that it depends on the game. I play most of my games at 40 on the Deck and I have been more than happy with it.
6. I take it to work everyday, use it in the bathroom, and use it in the lounge while we watch TV. I bought the Jsaux dock for my office at work so it's being used heavily. My Steam backlog is nuts and this thing has allowed me to make a not insignificant dent in it.
7. Congratulations!