Smart 451 as a second car for commuting?

Dear Smart Community, I’ve been in love with a smart for a long time. Now it may soon become reality due to diesel driving bans in Stuttgart from 2019? The starting point: I commute 90km daily (back and forth), 90% expressway, limited to 80km/h. Often also traffic jams or stop and go. As a current vehicle I have a Passat Built 2007 TDI with 200,000km. From 2019 I can no longer go to Stuttgart. A large vehicle is mandatory due to family. Since a new EURO 6 diesel is currently simply too expensive for me, I think about keeping my passat and in addition to get a smart petrol truck to the office. (second model series). What do you mean? Does it make sense? What are recommended engine variants? How high is the fuel build? What is the cost of the smart in tax and insurance?