I've made some good Kolsch with 90% lager malt and 10% wheat malt, also tried without the wheat malt and it too was a good result. I used Perle hops with about 27IBU with no aroma hops, tried a 20l batch with 5g Perle last 5 mins of boil but it's a coin flip to which was best.
I fermented with Danstar Widsor, I know it's not a proper Kolsch yeast but it works.
Fermented at about 18°C to a few points off final gravity then raised to 20°c for a few days, crashed to 5°C for a day then added gelatine finings then kegged and lagered for 6 weeks.
It takes about a week for it to settle and pour clear in the keg as I find Windsor yeast is difficult to get to drop, I bottled some and it clears bright given time.