For most cars for auto starting you would probably have to have wires hooked up to turn on the following...
Fuel pump would need tobe turned on.
then starter motor would also have to hooked up to turn the car over.
I am not sure if something like this is easily done on your car, but I would assume it can be done since you don't have the smart key system.
With all the electronics in your car it would probably be more time consuming because of having to locate wires.
Some aftermarket alarm systems come with the ability to do remote starting, but again it has to be wired into the electrical system regardless.
Mercedes might have some special anti theft devices that require the key be turned to prevent theft via hotwiring etc. essentially I thinnk that remote starting is basically like hotwiring the car.
I would check with a local car alarm shop, not places like good guys/circuit city, but places that specialize in high end car audio and multimedia systems that also do alarms.
I would also make sure that they have done it on a car like yours before. You don't want someone trying it if they have never done it.
Hope that helps you on your quest.
P.S. i'mnot a tech, but above is what I think it would require.
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.