The more cylinders in a diesel engine, the quieter it will run.
Always kill a diesel engine before turning off the key. You can blow out diodes in the electrical system if you don't then you'll have other problems to deal with. Killing a diesel engine means shutting off the fuel supply whether it is pulling the throttle all the way down, pulling a knobbed cable or pushing a kill button.
There are better in mast furling systems than others. I have worked with many and I think Selden makes the best. I have used many and have installed them to replace conventional masts. Any piece of equipment on a boat requires cleaning and lubrication, but the components on Selden rigs have great quality control and work easily as long as the luff tension is not too loose, etc. I have seen great mainsails built for in mast systems that work really well and are functional even for windward performance.
Call a local air conditioner repair guy to deal with the loss of coolant. He/she can find the leak, repair it and make it right with little fuss for you except for writing the check.
You mentioned furler problems, of which you aren't very specific, but again, Selden's Furlex is, in my opinion the best out there. They are also very helpful with trouble shooting, My experience is it rarely is the system itself (as long as required maintenance is completed - and it doesn't require much), but rather the operator.
It's all a learning curve, but learn and enjoy your boat