I'd keep the Plus 8, dump both the Tesla and the Merc, and buy an EV that doesn't carry such a price penalty for having a "desirable" badge on it and with a decent 300 mile range, something like a VW ID4 or Hyundai Ioniq 5.
That way you have a fast touring car with unlimited range that, although it has faults, they are ones you know about and can work to improve. The EV would give you a daily driver that is cheap to buy & costs peanuts.to run, enables you to visit places (and there an increasing number of them) that have ULEZ restrictions in place, and has sufficient range for 99% of your usage.
If it turns out that you need a largish car for occasional 500-mile plus journeys that wouldn't be feasible in the Mog, just hire something for a couple of days.
