A dealership should be able to troubleshoot your alarm with a scanner tool.
The owner's manual says this about oil viscosity:
As for long term storage, there are a couple of things to think about... First, as the engine is run and the oil gets older, it carries combustion deposits in it and other contaminants. Including harmful acids, sulphur and stuff that to a small degree causes corrosion in the metal parts it gets in contact with. Not a major concern if the oil only had maybe 1-2 thousand miles on it and you change it before you return the car to service.
Second, as the car sits, moisture will condensate inside the engine just due to the ambient air humidity and temperature changes. So in essence, there will be water in the engine, which you can mostly get rid of by changing the oil before returning the car to service. If the ambient air/climate is pretty much stable where you store the car, it may not be a big issue. But hot days, cold nights, lots of rain one day/week and dry heat the next, you get moisture buildup. In fact, you ALWAYS get it, but driving the car daily gets rid of it because a fully warmed up engine makes it evaporate and it gets sucked out by the crankcase ventilation system. When you park the car for a longer period of time, nothing is there to heat it up to vapor or suck it out.
So the storage oil change answer kind of depends on what the storage location is like.
I personally would change the oil before returning the car to service.
I would also try to go and run the engine to normal operating temperature once a month or so if possible. Just to keep things fresh and oiled up, and to avoid leaving things like valve springs compressed in the same position for too long. Not real critical for a few months of storage, but if you want the best for the car...
And the trickle charger is the way to go. You don't want the battery to run down. You shouldn't disconnect it either. The radio memory settings and main computer always draw a little power, you can't turn all power consumption off. I think the battery can stand maybe a month of sitting, before it starts getting a little too low for comfort. A couple of months is enough to run it low enough that the car won't start. You don't want to let a normal lead-acid battery to get even half way down, it will never be the same again. Keep it charged.