Just a couple of quick items that are covered in more detail in other threads:
Go slow .... do not make anything worse.
Drain the fuel tank and disconnect the fuel pump until you need fuel.
Try to turn the engine by hand with a socket on the front crank bolt. If it will turn (you are lucky), remove the spark plugs and spray in WD40, if not, spray in a lot of PB Blaster (penetrating oil available at most auto stores) and try to rotate the engine twice a day until it brakes loose.
Once it turns, drain the oil and replace the filter.
Install a new battery; crank the engine until there is oil pressure.
Remove the fuel filter, pour in some fresh fuel, connect the fuel pump and pump a little fuel through the line to flush the fuel system.
The engine might start. After the engine runs, flush the engine coolant and replace with Mercedes yellow collect (expensive but worth it).
Before driving, test the brakes. Replace the rubber hydraulic hoses. Flush the brake fluid. It is more important to stop than to go.
Jim Villers
190SL, 230SL 5-Speed, 190E 2.3-16 Kompressor