these 203 series C-class like to have a new battery every four years, how old is your battery?

your A/C problem sounds like a simple pressure issue, and the EC light coming on is a failsafe mode designed in.

the car will warn you when too much oil is in the engine - get it down to the right level pronto.

Actually seems like your car is in pretty good shape, the A/C needs to be chked by a trained Mercedes tech.