Distractions are a big one. There are too many times I need to walk away from a problem to re-approach it later with a fresh perspective. We have a revolving office in a co-working space and I'm alone here most of this week. I've probably spent 4 hours cleaning it over the past three days, and not only has it helped me tremendously in organizing my thoughts, but the place is utterly spotless.
I completely agree on the working hours. I do have the benefit of being able to work at home, but 8-5 is killing me. If I don't exhaust myself at the end of the day, I can't easily fall asleep. If I can't easily fall asleep and have to get up to be "ready to start" at 8, don't expect me to be productive until around lunchtime... in which then it's lunchtime. So really, don't expect me to be productive until nearly 1PM unless there's a gun to my head. I haven't solved the sleep issue since I was 13, so that's not going to fix itself any time soon. However we can change the hours to be more around when I'm productive, or relax the hours (the process) and emphasize the result.
#3 and #11 are equally important to me. I need to make some very difficult design decisions that will be very expensive if they're wrong. I don't want them to be wrong and add additional cost somewhere -- whether it be correcting it down the road, or designing something that no one ever uses.