I had a LOT of trouble with the Kolsch I tried - literally everything went wrong. John, my LHBS guru was forced to try a bottle to tell me where my error was, and he just couldn't pin it down: it was skanked, oxygenated, the temperatures were off, there was an infection, AND I picked a bad recipe. So tip of the hat to you for brewing the style that I'm STILL afraid of!
As for fermenting temperatures. . . Kolsch is often advertised as a hybrid style that can tolerate higher temperatures. The truth is - in my OBSERVATIONAL and not PERSONAL experience - that GOOD Kolsch is brewed at ALMOST lagering temperatures. Higher temperatures result in weird off-tastes. So yes - get your temperatures as low as possible, and the yeast will stay happy.
As for carbonation in the bottle: don't worry about it. Plenty of yeast will make it into the bottle when you rack. If you keep the temperatures TOO low, the yeast will become dormant and, when you try a bottle in two or three weeks, it'll be flat. If that happens, just raise the bottle temperatures by ten degrees, and try again in a week. Keep raising the temperature until the yeast wakes up. So, in short - even if you don't believe me/us, you won't be hurt by trying the lower temperature fermentation. But if you go with the HIGHER temperatures. . .