1) I have trouble focusing in right before performance. I don't quite think I have the proper conception of what should be on my mind as I walk towards the piano and sit down, before I set myself.
I have a ritual I go through before I sit down to play to help build my focus and concentration. I have a handkerchief that I wipe the keys with and then I sit with my hands folded across my chest leaning over the keyboard and taking yoga breaths. I never, ever start playing until I can hear some of what I'm going to be playing in my head because I know that is when my concentration is going to reach its peak. Then, I start.
2) One of the professors at my school mentioned that I had a soloistic approach to the piano, but what I lack that some of the colleagues I look up to have is control- I still have a tendency to rush, especially away from slip-ups. Beyond tempi, my dynamic plan sometimes goes to ashes during my performance, and I feel that sometimes, I don't get the shades of dynamics that I want during performance.
I have the same problem with rushing. My performances are always faster than my practices, and that's something I've just had to get used to. When I'm warming up before I perform I always practice SLOW and QUIET for maximum control. It also helps to have a "flawless" mental image in your head of what you want to be doing. And when you make mistakes, don't let it upset you. Just keep going like nothing happened. It might help to practice this. Like play straight through the piece with no stops and force yourself (with metronome if you have to) to keep going even if your finger slips. Talk to yourself (ok, I know how this sounds but bear with me
) and tell yourself that "No, You are NOT Going to Rush When You Make a Mistake" over and over again.
Don't stress/obsess/worry/change dynamics in a performance. You know what you've been practicing and you'll naturally do it without having to think too hard about it. Another tidbit stressed to me by an old teacher: don't just think, oh, here's a (for example) crescendo to a forte. FEEL IT with your whole being. It makes a much more convincing performance.
In your normal practice (not before performance warm ups for sure!) push the limits of your control in both directions (fast and slow). Of course don't do this all the time but a few times helps. Often I find the slower I can go and still have a clear mental image of what I'm doing, the more I know/have control over the piece. As for practicing fast, it just helps to be prepared so IF you do rush so the piece doesn't fall to schimtereens.
When I perform, I have (roughly) ten different tempos I can take and adjust them according to the concert hall, my mood, and the audiences' mood.
Hope this helps and Happy Holidays!