did you get this sorted in the end ?
265/50/20 keeps the rolling diameter the same i believe so 255/50 will be slightly less but this will only affect the speedo slightly and nothing else.
What do you mean by street look ?
I would recommend you stick to 9" wide (reduce the weight) get the right offset 30-35
Tyre pressure sensors are cheap after market these days (around 200 for a set) and may not be worth the hassle of reusing your old ones (i didnt).
You may have already got yourself a set so post up some pics