Comfortable car for the field clerk – used purchase?

Servus dear automobiles, I have a job change: out of the office, into sales, on the road, where the car becomes practically my second home. The type of work is expected to be employee and independent sales representative at the same time (of course for different companies). The company offers an A6 or A4 station wagon as a business car. However, I myself am a big BMW fan and have long loved the E65 7 with a V8. This one is needed for around 12 years. .000€ incl. “CarGuarantee” on the market. With tax law, I still know almost nothing about it. Therefore the question to you: 1. Does it make economic sense to get the used 7er and not to accept the business car of the company and to have it paid out in cash? 2. Can the purchase price / running costs of the used 7er’s be taxed somehow, if one uses the as independent predominantly (90%) business? Best regards Stephan