I'm not 100% sure about using a charger designed to be attached to the battery via the cigarette lighter. But you won't have any trouble using one designed for the cigarette lighter, and you will find the doors have a small indent to accommodate the cable. Also, your '03 should have a way to provide power to unlock the trunk by attaching jumpers to the door frame, and a small piece that pulls out inside the fuse box.
If you plan to let the car sit for a long period of time it's always a good idea to leave the hood popped. Also, there is a manual release cable for the hood behind the right front wheel (passenger side in the US), but it is a pain to access. A lot of people route the cable to the back of the front tow cap for easier access, however that requires removing the bumper.
