Leasing Newbie/unclear KM/a

Hi, everybody, I’m about to make a decision when I buy my next car. Now there are a few questions I can’t answer so far. 1. I expect to drive more at the end of this year or next year because of work than now. I’m currently driving about 15,000 – 20,000 km a year, next year it could be about 60,000km. But that’s not yet certain. I know you can increase the km performance during the contract with many leasing contracts. Can I also “reduce?” 2. It will probably become a diesel – that’s why I tend to lease (due to current political developments and “diesel panic.”) I could theoretically buy the car also in cash. (approx. 35-40k€) What’s smarter? mMn Leasing currently, because I’m taking the thing off and I don’t care how much it’s still worth. 3. Financially, the whole thing is “secured.” I’ve never leased a car, and I don’t know what to think about it. I don’t feel like it. So I would like to put the total leasing costs right at the beginning on a 2nd account, from which the rates are always debited, and I don’t get any more of them, so to speak. Is there any reason not to do so? 4. My current car should still bring about 7000 euros, that I would then pay along with the tax refund as a special payment, since I no longer have this money “on the screen”. That would make 100% of my monthly obligations. About 10-12k€ of total leasing costs stay for 3 years. I have loosely over. It remains the problem with the expected km-performance. Do you have here tips or are the leasing banks so flexible that my concerns are unfounded. Thank you for your answers.