A couple of us answered the question over on the Yahoo site. But just to explain in a bit more detail:
On my boat there is a vertical rocker switch for the genset. The upper position is labeled start and the lower position is labeled stop. Holding the stop position engages the glow plugs.
The on-off switch that you are referring to is probably the genset breaker. It is protected by a slide which keeps the shore power breaker being engaged at the same time and functions like a transfer switch.
When I start my genset, I always start it with that breaker off. I let it warm up for a few minutes and then turn it on with all other sub breakers off. Then I wait until the Freedom 20 control panel ramps up and starts charging the batteries. I let that load the engine a bit- as much as 10 amps AC if the batteries are down, before I add more significant loads like the stove or water heater. If you don't have a Freedom just let it warm up for 3-4 minutes before putting significant load on it, just like you would do with your propulsion engine.
BTW a great modification that looks great and only costs $300 is to replace that resistance element stove top with an induction top. Here is a link to Amazon: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
The cooktop is more efficient than a resistance top and automatically splits the 15A incoming power between the two burners. On my resistance top it would trip the breaker if I turned both burners to high. You do have to use steel bottomed cookware, but no big deal on the boat.