As to the trunk not opening, you're probably not aware that the trunk lock button has a couple of different positions tied into the central locking system. Just insert the key and rotate 90 or 180 degrees or whatever and that should take care of that.
The "check coolant level" message is a rather common anomaly, having to do with surface corrosion on the prongs of the sending unit, located I think at the base of the expansion tank. I think you pinch the two clips on the side and remove it for cleaning, but I can't fully remember. In any event, it's a false reading.
Your ambient temperature sensor is either missing or broken. I think it's located by one of the fog lights, but not sure. Won't affect driving.
As to warning signs from a failing fuel pump, you might hear a whirring sound upon starting the car indicating it's on its way out. Generally though, I think they just fail without notice.
If the car requires some prolonged cranking to get started, it could be plugs, injectors, I'm not sure perhaps even crankshaft position sensor, and perhaps a lot of other things. It would help if you had service records or somehow knew what was last done on the car and when, it sounds as if it might need a thorough going through of the basics.