USB 3.0 works just fine. Read/Write speeds have easily been over 30MB/s, with peaks around 40 or so. That's with the Sandisk 64GB MicroSD Class 10 card I have installed, which is really the "bottleneck." It's noticeably faster using internal storage and much closer to max USB 3.0 speeds, especially when reading.
Also FYI, the included charger has an Output of 5.3V / 2.0A. Which is 10.6 Watt.
Keep in mind that the tablet can easily draw more power than either USB 2.0 or 3.0 can provide, while in use. USB is 0.5A and USB 3.0 0.9A. Using the included 2.0A charger is your best bet.
I just let mine charge up over night, so I'm not really watching it or anything. I haven't gotten anywhere close to killing the battery, but I also haven't put it through "all day" heavy use yet.
I am running GSAM, so we'll see how things look soon enough.