Well I love these sort of engineering projects (and I don't question people's motives for a cool project). I think the W124 would a good choice. If you plan on mounting the batteries in the floor, then the floor might need to be strengthened to support the additional weight. Obviously the SLS would have to go, it would just be a needless drain on the batteries, and contrary to what people might tell you, you can create a comfortable suspension setup with conventional springs and shocks. Hydraulic/air/electric gimmeckery is just that, gimmeckery that offers much more in complexity than it does in actual solving of problems (oh nooooo, my headlights point 0.0001 degrees higher because I put a carton of milk in the trunk, damn it, I wish I hadn't deleted my SLS).
The reason I think it would be a good chassis to begin with is because you could still get most of the truly needed luxuries from a mercedes, without having to put up with various incompatible electronic modules / CAN bus communication problems / DAS / Proprietary this / Patented that. So what does that leave to be figured out? (Apart from the entire powertrain) You would need electric power steering and an electric A/C compressor. Heating would also be questionable, but what I would absolutely looooove to see in a car is a heat-pump. Imagine that, you get in your car in the middle of winter, and it starts heating right away! No need to wait for engine to warm up or whatever. Why hasn't anyone put a heat-pump into a car before??? By the time the condenser would freeze over, the engine would be warm enough and the system could be temporarily reversed back in A/C to thaw the condenser and restore airflow to the radiator.
Anyway, big project, I'd love to see it happen. PM me if you need ideas, I love these sorts of projects, and I'm full of good ideas.
I hope the local electricity isn't derived from a fossil fuel, otherwise I hope you realize that you're not solving the problem, you're just shifting the blame (not meant as a personal insult to you, a lot of EV drivers don't realize that the energy they put in their cars comes from a much dirtier source than an ICE). It's basically a classic case of let's clean up the city by moving pollution to the countryside where the coal burning plant is located.
Good luck.